7 Measurements, Dose Calculations, and System Design for X ...

Read chapter 7 Measurements, Dose Calculations, and System Design for X-Ray Backscatter Advanced Imaging Technology Systems: Passenger screening at commer. AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards (2015) Chapter:7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems GetThisBook VisitNAP.edu/10766togetmoreinformationaboutthisbook,tobuyitinprint,ortodownloaditasafreePDF. Lookingforotherwaystoreadthis? INADDITIONTOREADINGONLINE,THISTITLEISAVAILABLEINTHESEFORMATS: PDF FREE Download Paperback $69.00 AddtoCart Ebook $54.99 AddtoCart MyNAPmembersSAVE10%offonline. NotaMyNAPmemberyet?Registerforafreeaccounttostartsavingandreceivingspecialmemberonlyperks. Nothanks.I’llkeepreading Contents Chapter Page of184 OriginalPages TextPages GetThisBook «Previous:6ReviewofX-RayBackscatterAdvancedImagingTechnologyStudies Page86 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel 7 Measurements,Dose Calculations,andSystemDesign forX-RayBackscatterAdvanced ImagingTechnologySystems Thischaptercontainsthemeasurementproceduresdevelopedbythecommittee,includinghalf-valuelayer(HVL)measurements,percentdepthdose(PDD)measurements,airkermameasurements,anddeterminationofthekermaperscreeningoutsidetheinspectionarea.AfterthesectiondescribingthemeasurementprocedurestherefollowsthemeasurementresultsacquiredbytheNationalResearchCouncil(NRC)1subcontractorfortheRapiscanSecure1000advancedimagingtechnology(AIT)systemandtheAS&ESmartCheckAITsystemandthecommittee’sreviewofeachsystem’sdesign.Thenextsectionmakesuseofthemeasureddataforthedosecomputations.ThedosecomputationsincludedescriptionsoftheX-raysourceterm;featuresofthereferenceAITsystemused;validationofMonteCarlosamplingprocedures;descriptionofthepassengerirradiationgeometry,includingphantoms;anddosimetryresultsforstandardscreeningconditions.AdditionalinformationextractedfromthedosecomputationsincludevariationsinX-raytubevoltage,dosetoradiosensitivecellsintheskin,andfailuremodeanalysis.Thechapterconcludeswithfindingsandrecommendations. EvaluationofeffectivedosefromanunknownX-raysource,suchasanAITscanner,canbeaccomplishedbymeasuringHVL,depthdose,andairkermaandthenusingtheHVLanddepthdosedatatocalculatethephotonspectrum.Withthephotonspectrumandasuitablemathematicalmodelofthepersonbeingscanned, _______________ 1EffectiveJuly1,2015,theinstitutioniscalledtheNationalAcademiesofSciences,Engineering,andMedicine.ReferencesinthisreporttotheNationalResearchCouncilareusedinanhistoriccontextidentifyingprogramspriortoJuly1. Page87 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel MonteCarlocalculationscanbeusedtodeterminetheorgandoseperincidentphoton,andtheeffectivedoseperphotoncanbecalculatedusingorganweightingfactors.Finally,themeasuredairkermacanbeusedtodeterminethenumberofincidentphotonsand,therefore,theeffectivedose.TheANSIreferenceeffectivedose(EREF)isdeterminedthroughasimplemathematicalrelationship2basedonmeasurementsoftheHVLandairkerma. MEASUREMENTPROCEDURES TheNationalResearchCouncil(NRC)subcontractorDavidHintenland,AdvancedLaboratoryforRadiationDosimetryStudies,J.CraytonPruittFamilyDepartmentofBiomedicalEngineering,UniversityofFlorida,performedfieldmeasurementsofHVL,PDD,airkerma,anddoseoutsidethescanningareafortwoAITsystems:(1)theAS&ESmartCheck-HTdual-posesystembeingevaluatedattheTransportationSecurityAdministration(TSA)SystemsIntegrationFacility(TSIF)and(2)aRapiscanSecure1000single-posesystemlocatedattheNationalInstituteofStandardsandTechnology(NIST).Bothsystemsoperatewithanappliedvoltageof50kV,althoughtheyusedifferentX-raytubes,anodecurrents,andscanmechanismsandscanrates. MeasuringHalf-ValueLayer Background TheHVLinaluminumprovidesacommondescriptionforcharacterizingthespectrumofanX-raybeam.Withtheadditionofaluminum,thelower-energycomponentsoftheX-rayspectrumarepreferentiallyattenuatedandcreateadifferencebetweenthefirstandsecondHVLs.MeasuredvaluesofthefirstandsecondHVLswereutilizedtocharacterizetheenergyspectrumoftheAITsystems.Theattenuationcurveinaluminumwasevaluatedinincrementsassmallas0.05mmofaluminum(mmAl)acrosstheexpectedrange.ThisnotonlypermittedthefirstandsecondHVLstobeextractedfromthedatabutalsoprovidedacontinuouscurveoftheattenuationinaluminumagainstwhichtheX-rayspectrumofthesimulatedX-raysourcetermcouldbepreciselymatched. _______________ 2FormulasforcalculatingEREFareprovidedinSection6.1.3ofAmericanNationalStandardsInstitute/HealthPhysicsSociety(ANSI/HPS),“RadiationSafetyforPersonnelSecurityScreeningSystemsUsingX-RayorGammaRadiation,”ANSI/HPSN43.17-2009,2009,http://hps.org/hpssc/index.html. Page88 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel ExperimentalApproach HVLmeasurementsweremadeutilizingaKeithleymodel96035b15ccparallel-plateionchamberinterfacedwithaUnivisionelectrometerfromPTW.3Theionchamberhastwowindows.Thethinnerwindow,32mg/cm2or320µmtissueequivalent(mammographyfocus),wasutilizedforcharacterizingtheHVLsoftheexpected,relativelysoftX-rayspectrumgeneratedbytheAITsystems.ThedeterminationofHVLrequiresaseriesofmeasurementsofbeamintensityperformedwithincreasingaluminumattenuatorthicknessesrelativetotheunattenuatedbeamintensity.Anabsolutecalibrationofthechamberisnotcriticaltothemeasurementresults.Thechamberwas,however,calibratedtoamolybdenum/molybdenumtarget/filtermammographyX-raystandardat28kV. Toobtainimprovedsignal-to-noiseratioforthissetofmeasurements,bothtypesofAITsystemswereoperatedinapartiallyfixedscanningmode;inthismode,onlyoneAITsystemmodule(eithertheanteriorortheposterior)isoperatingforaseriesofmeasurements.Themodeispartiallyfixed,meaningthattheverticalmovementoftheX-raysourceisstoppedbutthehorizontalisnot;hence,onlyaline,andnotanentirearea,isscannedbythepencilbeam.Theservice/engineeringmodewasutilizedtoperformmeasurementswiththeX-raytuberaisedtoafixedverticallocationwhilethebeamcontinuedtoscaninthehorizontaldirection.AlthoughtheX-raysourceandassociatedbeam-formingequipmentgeneratesapencilbeam,thecontinualhorizontalscanningatafixedverticallocationresultsinirradiatingaverticallineorbandacrossthefaceoftheionchamber.Althoughonlyaportionofthechamberisexposed,thesameportionisexposedforeachattenuatorthickness,andallmeasurementsarereferencedtothesamegeometryexposurewithnoattenuatorpresent.Aseriesofatleastthreereplicatemeasurementsweremadeforeachattenuatorthicknessundertheseconditions.Sixreplicatemeasurementsweremadeforanaluminumattenuatorthicknessesoflessthan0.6mm,wheretherelativechangeinexposureisexpectedtobethegreatestduetothefactthatthethinattenuatorsaffectthelow-energyportionsoftheX-rayspectrum. ThecoordinatesystemfordescribingmeasurementsontheAITsystemsissetupalongthecentralmedial(longitudinal)axisofasubjectundergoingthescanningprocess,whichwasdefinedasbeingcollocatedwiththegeometriccentralaxisoftheAITsystem.ThispositionisdesignatedintheCartesiancoordinatesystemasx=0cm,y=0cm,wherexisthedimensiontowardorawayfromtheanteriorX-raysource(−xisclosertothesource),andyisleftorrightasthescreeningsubjectfacestheanteriorsource(−yistotheleft,+yistotheright)(Figure7.1). FortheHVLmeasurements,the15ccparallel-plateionchamber(approximately4cmindiameter)wascenteredintheAITsystemhalfwaybetweenthe _______________ 3SeethePTWFreiburgGmbHwebsiteathttp://www.ptw.de,accessedJanuary13,2015. Page89 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel FIGURE7.1ThecoordinatesystemfordescribingmeasurementsontheAITsystems.Xisthedimensiontowardorawayfromtheanterior(darkgray)X-raysource(−xisclosertothesource),andyisleftorrightasthescreeningsubjectfacestheanteriorsource(−yistotheleft,+yistotheright),+zispointingupward,withz=0atthebaseoftheAITsystemmodules. entranceandexitportals,atx=0cm,andcenteredbetweentheanteriorandposterior4(ortransmissiondetector),aty=0cm.TheverticalpositionofthechamberwasadjustedbytrialanderrortocorrespondwiththepositionoftheX-raybeamandcorrespondinglyprovidesthegreatestsignalresponsebyhavingthemaximumexposedchamberarea.Thebeamwasfurthercollimatedbyutilizingasheetofleadthatwascustomfittedtothechamberandlocatedbehindthealuminumattenuatorstoreducescattercontributionsfromthealuminumattenuatorsandtoprovidenarrowbeamgeometry. _______________ 4ThisisthecasefortheRapiscanSecure1000;fortheAS&EAITsystem,themanufacturer’ssuggestedposition(footprints)wereused. Page90 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel MeasuringPercentDepthDose Background Percentdepthdose(PDD)profilesarearelativemeasurementofdoseasafunctionofdepthintotissue.5PDDisdefinedasafunctionofdepthintissuemaintainingaconstantsource-skindistance(SSD),althoughitismorepracticaltodirectlymeasurethetissue-maximumratio(TMR),wherethereferencedepthremainsconstant,andsubsequentlytransformtheacquireddatatothePDD.OneobjectiveforthePDDmeasurementsistoelucidatetheskindosethatmaybedeliveredtoradiobiologicallysensitivelayersoftheskinsuchastheepitheliallayer.AnotheristoproviderelativePDDdepthprofilesthatcanbeusedtovalidatethecomputationallydeterminedradiationdosestotheradiobiologicallysensitiveregionsoftheskin.TheshallowskinlayersforwhichthesemeasurementsaredesiredpresenttechnicalchallengesduetothelowenergyoftheX-raysourcesofinterest,requiringthatthinlayersoftissue-equivalentmaterialsbeproducedandthatmeasurementsbemadeusinganionchamberwithaverythinwindowinordertominimizesecondaryelectronproductionpriortotheX-raybeam’sreachingthesensitivevolumeofthechamber.Tominimizetheeffectsofdosebuildupattheserelativelylowenergies,itisimportanttoutilizeanionchamberthathasaverythin(andthereforefragile)entrancewindow.Suchchambershavesmallvolumes(afewcubiccentimeters),however,sothattheentrancewindowdoesnotbreakfromthedetectorbeingmovedandhandled,withresultinglowsensitivity.TheNRCsubcontractorselectedaCapintecPS-033parallel-plateionchambertoperformthesemeasurements.Thischamberprovidesathinmylarwindow(0.5mg/cm2or5µmtissue-equivalentthickness)andarelativelylargesensitivevolume(4.9cm3)forachamberofthistypewithadiameterof2.5cmandatotalthicknessof1cm.ThePS-033parallel-plateionchamberwasintegratedwithaPTWUnidoseelectrometerforthissetofmeasurements.BecausethePDDmeasurementisarelativemeasurement,thechamberwasnotcalibratedaheadoftime,althoughtheresponseat50kVwaswellcharacterizedbytheNRCsubcontractorandcomparedtootherparallel-plateionchambersusedinthisstudy. TodevelopthePDDcurves,itisnecessarytohaveatissue-equivalentmaterialofappropriatethicknesses.Fora50kVX-raysourcewithlittlefiltration,quitethinlayersoftissue-equivalentmaterialarerequired.TheNRCsubcontractor,therefore,fabricatedcustom-madelayersoftissue-equivalentmaterialsandatissue-equivalentphantom-blockinwhichthethin-windowionchamberwasembedded.Thelateralextentofthephantom-blockis10cm×10cmwithanadditional5cmoftissue-equivalentmaterialbehindthechamberinorder _______________ 5Thedosevaluesaredividedbythemaximumdose. Page91 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel tocapturethescattercontributionstothePDD.Thesubcontractorfabricatedaseriesoftissue-equivalentmaterialthicknessesasthinas25µmandupto10mmthick.6Theprecisethicknessofthetissue-equivalentslabswereindividuallydeterminedbymeasurementsperformedwithananalogdialindicatorwith25µmincrements.7Thetissue-equivalentmaterialswereevaluatedagainstseveralothercommonlyusedphantommaterials,includingBR12(abreasttissue-equivalentmaterialhavingalowerdensity)andacrylic(aplastichavingahigherdensitybutlowerattenuationcoefficient),at50kVintheNRCsubcontractor’slaboratory.Thematerialsproducedperformedasexpectedrelativetothesebenchmarksandweredeterminedtohaveadensityof1.04g/cm3,matchingthatofskinandsofttissue.ThesematerialspermittedthedevelopmentofaPDDfrom0toover60mmwithhighspatialresolution. ExperimentalApproach ThegeneralprocedureutilizedforperformingthePDDmeasurementscloselyfollowedtheprocedureusedforperformingtheHVLmeasurementswherethetissue-equivalentmaterialwasusedinplaceofaluminumsheetsandwithnoleadcollimationfortheionchamber.Inordertomaximizethesignal-to-noiseratioforthissetofmeasurements,theAITsystemwasoperatedinapartiallyfixedscanningmode(describedindetailunderthesection“Half-ValueLayerMeasurements”).Thiswasparticularlyimportantforthissetofmeasurementsbecauseofthesmallphysicaldimensionsofthethin-windowchamber.Aseriesofatleastthreereplicatemeasurementsweremadeforeachattenuatorthicknessundertheseconditions. AnadditionalsetofPDDmeasurementswasmadeusingtheKeithleymodel96035b15ccparallel-plateionchamberwiththelow-energy(32mg/cm2)windoworientedtowardthebeamforcomparisonwiththePS-033chamber.Whilethe15ccchamberhasarelativelythinwindowat32mg/cm2,itissignificantlythickerthanthe0.5mg/cm2windowofthePS-033chamber. Thethin-windowparallel-plateionchamber(approximately2.5cmininnerdiameter)wascenteredina10cm×10cmblockofphantommaterialwith5cmofbackscattermaterialbehindit.Thecenterofthechamberwaspositionedatx=0cmandy=0cm.TheverticalpositionofthechamberwasadjustedbytrialanderrortocorrespondwiththepositionoftheX-raybeamthatcorrespondingly _______________ 6ThecommitteeisnotfamiliarwithanypreviousstudythathassuccessfullymeasuredPDDcurvesattheselowenergies,inpartbecausetheycallforverythinlayersoftissue-equivalentmaterialstobefabricated. 7TheUniversityofFloridahasextensiveexperiencewiththedevelopmentandfabricationoftissue-equivalentmaterialsanddevelopedthesematerialsspecificallyforthisapplicationandinordertoprovideempiricaldatathatcouldbeusedfortheverificationoftheparallelcomputationaleffort. Page92 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel providedthegreatestsignalresponsebyhavingthemaximumexposedchamberarea.Thiswasdeterminedtooccurforthecenterofthechamberatz=19.5cm. Inordertomeasuretheexposureasafunctionoftissuedepth,thedesiredthicknessoftissuewasplaceddirectlyinfrontoftheionchamber.A1cmairgapwasmaintainedbetweenthetissue-equivalentmaterialsandthechambertopreventinadvertentcontactandpotentialdamagetothethinwindowoftheionchamber.NotethatthegeometryselectedherediffersfromtheusualapproachtomeasurePDDbecauseofexperimentalpracticality.Toassureaccuracy,thedetectorblockwasnotmovedbackwitheachadditionallayeroftissuebutwaskeptatafixedlocation.ThedatawerethentransformedtothePDDbytheMayneordfactor,8whichinthiscasesimplifiestoacorrectionusingtheinversesquarelaw;becausethebeamisbroad,distancesarelargecomparedtothetissuethicknesses,andthescatterphantomareaisfixed. MeasuringAirKerma Background Airkermameasurementsprovideanabsolutemeasureoftheairkerma(inGy)atdiscretelocationsintheAITsystemX-rayfield.Thesemeasurementsprovideanabsolutereferenceagainstwhichanycomputationaleffortscancalibratetheircalculationsinordertopredictdosetothescannedsubject.IncontrasttothemeasurementsperformedforHVLandPDD,themeasurementofairkermaisperformedwiththeAITsystemoperatedinitsnormalscanningmode.Inthismodeofoperation,theX-rayexposureisquitelow,anditismostappropriatetousealarge-volumeparallel-plateionchambertoobtainthebestpossiblesignal-to-noiseratio.Correctionsfortemperatureandpressure,relativetothechambercalibrationconditions,areappliedtoensuretheprecisionofthesemeasurements. ExperimentalApproach AirkermameasurementswereperformedutilizingaKeithleymodel96020C150ccparallel-plateionchamberinconjunctionwithaPTWUnidoseelectrometer.TheionchamberwaspreviouslycalibratedusinganH60spectrum.9Duetothetimelimitationsofthisstudy,itwasnotpossibletoperformachambercalibration _______________ 8W.V.MayneordandL.F.Lamerton,Asurveyofdepthdosedata,BritishJournalofRadiology14:255,1941. 9TheH60spectrum,formedatNISTbyfiltrationusing4mmAland0.61mmofcopper,wasusedforairkermacalibrations. Page93 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel usinganM5010spectrumuntilafterallthemeasurementsweredoneonbothX-raybackscatterAITsystems.However,thepostcalibrationallowedforacorrectionofallaffecteddatasothatnoincorrectvalueswereusedorincludedinthisreport.TheM50isexpectedtobemostrepresentativeofthebeamforboththeAS&ESmartCheckandtheRapiscanSecure1000AITsystemsthatweretested. Measurementsfortheairkermawereperformedwiththeelectrometeroperatedinintegratingmodeoverthecourseofanormalscreeningsubjectscan.Thetotalcharge(picocoulombs)wasrecordedforeachcase.Thechargewassubsequentlyconvertedtoairkermausingtheappropriatechambercalibrationfactorandmakingairtemperatureandpressurecorrectionsrelativetothechamber’scalibrationconditions. Foreachoftheairkermameasurements,the150ccparallel-plateionchamberwascenteredatx=0cm,y=0cm,withtheverticaldimension(z)referencedtoz=0cmatfloorlevel.Airkermawasmeasuredatfourverticallocations:z=32cm,z=120cm,z=150cm,andz=202cm.Themeasurementlocationsweredesignedtoroughlyevaluateanyvariationsinbeamintensityasthebeamscansvertically.Becauseofthelowintensityofthescanningbeam,aseriesof10individualmeasurementswererecordedateachverticallocation.11 DeterminationoftheKermaperScreeningOutsidetheInspectionArea Background InviewoftheuniqueconditionsoflowX-rayenergyandexposuretimesontheorderofafewseconds,typicallow-dose-ratesurveyinstrumentsarelimitedintheirabilitytoaccuratelyrespondtothesefields.Inordertoaccuratelydeterminetheexposureoutsideoftheinspectionarea,theNRCsubcontractorutilizedalarge-areaparallel-plateionchamber(Keithleymodel96020C,150cc)interfacedwiththePTWUnidoseelectrometer. Inordertoaccuratelyaccountforthescattercontributionsfromthepassengerbeingscreened,ascattermediumthatsimulatesthepresenceofthehumanasascattersourcemustbeincluded.Avarietyofscattersourceswereconsidered.TheUniversityofFloridahaspreviouslyconstructedaseriesofanthropomorphicphantomsrepresentingavarietyofhumananatomies.Thefullhuman-sizedphantomisconstructedoftissue-equivalentmaterialsdesignedtomimictheresponseof _______________ 10TheM50spectrum,formedatNISTbyfiltrationusing1.07mmAl,wasusedforairkermacalibrations. 11Notethatthereisaplatformthatcanbeinsertedintothescreeningsystemthatscreeningsubjectswouldnormallystandonthatis14cmtallatitsmidpoint.Thus,thebottomofsubjects’feetwouldbeatz=14cmwhentheplatformisused.Theplatformwasremovedforthemeasurementsperformedinthisstudy. Page94 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel tissuesinthelow-energyX-rayrangeandincludesarealisticinternalanatomy.Thephantomdevelopmentanddetailsareavailableinthepublishedliterature.12ThesephantomshavebeenutilizedextensivelyforradiationdosimetrystudiesofclinicalX-raysystems.TheyarefabricatedasphysicalanalogstoselectedphantomsintheComputationalPhantomLibrary,accuratelyreproducingtheanatomyandincorporatingappropriatetissue-equivalentmaterials. Doseoutsidethescreeningareamayarisefromtwosources:radiationscatteredfromscannedsubjectstotheareaoutsidethescanningregionandX-rayleakagefromtheX-raytubehousingarea. ExperimentalApproach Foreachsetofmeasurements,alarge-areaKeithleymodel96020C150ccparallel-plateionchamberinterfacedwithaPTWUnidoseelectrometerwasused.Theelectrometerwasutilizedinintegrationmode13foreachofthesemeasurements.AFluke451Bsurveyionchamberwasalsopositionedincloseproximitytotheparallel-plateionchamberandwasoperatedinintegrationmodeutilizingthethinmylarwindow. Measurementsfortheairkermawereperformedwiththeelectrometeroperatedinintegratingmodeoverarepeatedseriesofnormalscreeningsubjectscans.Measurementswereperformedatseverallocationsoutsideofthesubjectinspectionareatoindividuallyquantifythecontributionsfromeachofthesesources,asdescribedbelow.Themeasurementsintegratedoveratleast40scansperformedateachofthemeasurementpositions.Thetotalcharge(picocoulombs)wasrecordedforeachcaseanddividedby40;inthisway,smallerchargescouldbemeasured.Thechargewassubsequentlyconvertedtoairkermausingtheappropriatechambercalibrationfactorandincludingairtemperatureandpressurecorrectionsrelativetothechamber’scalibrationconditions. Ameasurementlocationonthebacksideofthescanningunitwasselectedtoevaluateleakageradiationthatmaybeexitingtheunitinthatdirection.The150ccparallel-plateionchamberwaspositionedagainsttherearexterioroftheAITsystemassemblyataheightofz=150cm,centeredonthepaththattheX-raysourcetravelswhileverticallyscanning. Again,aseriesof40normalsubject-screeningscanswereperformedwhilethedetectionsystemscontinuouslyintegrated.Here,ananthropomorphicphantom _______________ 12J.F.Winslow,D.E.Hyer,R.F.Fisher,C.J.Tien,andD.E.Hintenlang,Constructionofanthropomorphicphantomsforuseindosimetrystudies,JournalofAppliedClinicalMedicalPhysics10(3):195-204,2009. 13Integrationmodeaccumulateschargeoveraspecifiedtimeandcanbemoresensitive,albeitslower,thantheratemode,whichdetectsthecurrent. Page95 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel representativeofanadultmalewasusedforthispurpose.Theregionfromthebottomofthepelvistothetopoftheheadwasusedasthescattersource.Thephantomwaspositionedonastoolsuchthatthebaseofthepelviswaslocatedatz=74cmandthetopoftheheadwasz=170cm.ThephantomwaspositionedsuchthatthecenterofthelongitudinalaxisofthephantomwascenteredintheAITsystematx=0cm,y=0cm. Theparallel-plateionchamberwaspositionedatthetwopositionsalongtheedgeoftheAITsystemexitonthesidetowardtheoperatorposition.Thedetectorwascenteredataheightz=120cmforeachscattermeasurement,essentiallyevenwiththemidpointoftheverticalextentofthephantom.Thelateralpositionswerecharacterizedbyx=0cm,y=−66cm,andx=−27cm,y=−66cm. AS&ESMARTCHECKSYSTEMMEASUREMENTRESULTSANDSYSTEMDESIGN Underthedirectionofthecommittee,theNRCsubcontractormademeasurementsontheAS&ESmartCheck(SerialNo.1004)AITsystemusingthesameprotocolusedfortheRapiscanSecure1000.TheAS&ESmartCheckAITsystemhasnotbeenapprovedbyTSAforairportdeploymentyet;thus,thesysteminspectedbythecommitteemaynotbethefinalversionthatmaybedeployedinairportsinthefuture. Half-ValueLayerResults MeasurementsofHVLweremadeatafixedheightusingaSmartChecksoftwarecommandthatcausedthetubeheadtocomeuptoafixedheightandoperateforthe3secondsrequiredforanormalscan.Thismodeofoperationrequiresapasswordthatwouldbeavailableonlytomaintenancepersonnel.Theverticalpositionofthisbeamwasz=19.5cm(withx=0cmandy=0cm).HVLmeasurementsprovidedhighlyreproducibledataandhighresolutionofspectralhardeningwithincreasingthicknessesofaluminumattenuators.ThedatapermitnotonlytheextractionofafirstandsecondHVLbutalsoadetailedattenuationcurveasafunctionofaluminumfilterthicknessthatcanbeusedtorefineestimatesoftheincidentX-rayspectrumforcomputationaldosedetermination.AggregatemeasurementsoftheHVLandassociateduncertaintiesaretabulatedinTable7.1and Page96 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel TABLE7.1Half-ValueLayerMeasurementsfortheAS&ESmartCheck AluminumThickness(mm) ExposureMeasurement(pC) Uncertainty(pC) 0.0 5.52 0.06 0.1 5.15 0.08 0.2 4.70 0.13 0.3 4.47 0.06 0.4 4.16 0.10 0.5 3.92 0.04 0.6 3.65 0.03 0.7 3.39 0.04 0.8 3.19 0.04 0.9 3.04 0.04 1.0 2.90 0.02 1.5 2.31 0.02 2.0 1.87 0.03 2.5 1.53 0.03 3.0 1.28 0.02 3.5 1.11 0.02 4.0 0.97 0.01 4.5 0.82 0.01 5.0 0.71 0.02 NOTE:Eachmeasurementistheaverageofatleastthreemeasurementscans.Theuncertaintyrepresentstheobservedstandarddeviationinthereplicatemeasurementsforeachaluminumthickness.pC,picocoulomb. graphicallyillustratedinFigure7.2.ThespecificvaluesthatareidentifiedasthefirstandsecondHVLsare1.1and1.7mmAl,respectively.14 PercentDepthDoseMeasurements ThePDDmeasurementsaretabulatedinTable7.2forthePS-033thin-window(0.5mg/cm2)4.9cm3chamberandillustratedgraphicallyinFigure7.3. Again,asecondsetofPDDdatawascollectedusingthelarger15ccparallel-plateionchamberwitha32mg/cm2windowthickness.AcomparisonoftheresponseforthetwochambersisillustratedinFigure7.4. ForthisAIT,standarddeviationsforeachsetofexposuremeasurementswere _______________ 14ThehighspatialresolutionoftheHVLdataforthinlayersofaluminumwillpermitthelow-energycomponentsoftheX-raybeamtobeincorporatedintoanycomputationalcandidatespectrum.Thus,thecompletealuminumattenuationcurvecanprovideimprovedfittingoftheX-rayspectrumcomparedtopreviousmodelsthatincorporatedsimplythefirst,andsometimessecond,HVL.ThisprocessandtheeffectsonthePDDsimulationprocessarediscussedinmoredetailinthe“MeasuringPercentDepthDose”section. Page97 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel FIGURE7.2High-valuelayermeasurementsasafunctionofaluminumthicknessfortheAS&ESmartCheck.Errorbarsarenotshownsincetheyareapproximatelythesizeoforsmallerthanthesymbols. calculatedbasedonthereplicatedatasetandaveragedlessthan2percentofthemeanvalue,thelargestbeing4.2percentforthethin-window(0.5mg/cm2)4.9cm3chamber.Forthe15ccchamber,thestandarddeviationforeachsetofexposuremeasurementsaveragedlessthan1percentofthemeanvaluewiththelargestbeing1.5percent.15 Itisimportanttopointoutherewhyextraeffortsweretakentoacquireextremelyhigh-resolutionPDDdata.BecauseconcernshavebeenexpressedthattheshortrangefordosebuildupatlowenergiesgeneratedbyanXraytube,withavoltageof50kVapplied,deliversapeakdosetoradio-sensitiveportionsoftheskinandthatthismaybegreatenoughtoproducesignificantriskofskincancer.AccuratePDDdataareneededinordertoinvestigatethisclaim.WhilePDDprofilesarecommonlycharacterizedforradiationtherapybeamsoperatedatmuchhigherenergies(inthe~10MVenergyrange),theyarenotcommonlycharacterizedforenergiesatwhichAITsystemsoperate.Thispresentsauniquechallengebecauseanypeakdosefor50kVsystemsisexpectedtooccuratveryshallowtissuedepthsandrequiresaspecializedionchamberhavingaverythinentrancewindow,which _______________ 15Uncertaintiesinthetissuedeptharesubstantiallysmallerthanthesizeofthesymbolsintheaccompanyingfigures.Hence,youmightnotseethemeventhoughtheyarethere. Page98 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel TABLE7.2PercentDepthDosefortheAS&ESmartCheckUsingthePS-033Thin-Window(0.5mg/cm2)4.9cm3IonChamber TissueDepth(mm) PDD(%) StandardDeviation(%) 0.0 92.2 3.6 0.0 91.7 1.6 0.2 93.5 1.6 0.3 89.8 3.2 0.3 92.6 1.6 0.5 99.0 1.6 0.7 100.0 1.6 1.0 92.4 4.2 2.0 92.2 4.2 3.1 88.3 1.6 4.2 79.9 1.6 5.9 77.7 3.2 8.0 67.4 1.6 9.6 56.4 1.6 15.6 44.1 1.6 20.4 35.8 1.6 26.2 28.3 1.6 31.0 20.4 1.6 40.7 14.9 1.6 51.4 8.90 1.6 62.2 7.88 1.6 minimizesproductionofsecondaryelectronsasthebeamentersthechamber,andspecializedphantommaterialstorepresenttissueattenuationandthethinthicknessesofinterest. Phantommaterialsweresuccessfullyproducedinthinlayers,assmallas25µm.Aseriesofthicknesseswerefabricatedin10cm×10cmcrosssectionssothatthesecouldbeassembledinvariouscombinationstodevelopthedataforthePDDcurves.ThePDDdatademonstratedapeakdoseoccurringatadeptharound0.5-0.7mm.Thepeak,however,isnotsignificantlygreaterthanistheentranceskindose—itexceedstheentranceskindosebyapproximately8percent.Consequently,thereshouldnotbeconcernthattheshallowdoseispreferentiallydepositedtoradio-sensitivelayersoftheskin. TheremainderofthePDDcurvedemonstratestheattenuationofthe50kVX-raybeamforthicknessesupto62mm.AfirstHVLof13mmandasecondHVLof15mmintissueisobservedforthisbeam.About10percentoftheentrancedoseisdeliveredatadepthof62mm. AsecondsetofPDDdatawascollectedusingthelarger-volume(15cc),thicker-windowionchamber.Thisdatasetprovidedenhancedmeasurementaccuracyoverallbutthesmallestrangeoftissuedepths.Whennormalizedtothe Page99 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel FIGURE7.3PercentdepthdosecollectedfortheAS&ESmartCheckusingthePS-033thin-window(0.5mg/cm2)4.9cm3ionchamber. maximum,thePDDcurvesfromthetwoionchambersmatchwithinthemeasurementuncertaintiesfortissuedepthsgreaterthan1mm.Atdepthslessthan1mm,thelarger-volumechamberdoesnotresolvethedosepeakduetothethickerwindowthatgeneratessecondaryelectronspriortotheX-raybeamenteringthesensitivevolumeoftheionchamber.Whilethiseffectmustalsooccurtosomedegreeinthethin-windowPS-033chamber,thecurvesdemonstratetheneedtoutilizeathin-windowionchambertomoreaccuratelyresolvethedetailsofthePDDcurveatthislowenergyandthistissuedepth. ThePDDdatawerealsousedasavalidationtoolforthecomputationalsimulations.Goodagreement(seeFigure7.13)wasobtainedbetweenthecomputationalandempiricalevaluationsofthePDDcurves. TheinitialsimulationswerenotparticularlygoodmatchestotheempiricalPDDcurves.ThroughaseriesofdiscussionsandareviewofboththeHVLandthePDDdata,itwasrecognizedthatthecandidateX-rayspectrumthatwasbeingutilizedbasedonpreviouslycollecteddatawasoverlyhard(i.e.,excessivelyfiltered,low-energybeamcomponents).Bydevelopingasoftercandidatespectrum(reducingthefiltrationtoincludemorelow-energycomponents),agoodmatchwasobtainedforbothHVLandPDDcurves.Thisdemonstratesthevalueofobtain- Page100 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel FIGURE7.4ComparisonofpercentdepthdosedatacollectedfortheAS&ESmartCheckusingthethin-window(0.5mg/cm2)4.9cm3chamber(greentriangles)andthe32mg/cm2window15ccchamber(bluecircles).Theinsetshowstheregionfrom0to8mmenlarged,indicatingapeakaround0.5to0.7mm. inghigh-spatial-resolutionmeasurementsforHVLandPDDcurvestoaccuratelycharacterizetheX-rayspectrumforAITsystems. AirKermaResults PersonBeingScreened Aseriesof10individualairkermameasurementsweremadeateachmeasurementposition.Eachmeasurementwasmadewiththeionchamberpositionedaspreviouslydescribed,andanormalsubjectscanwasmadealongthecentralaxis(x=0cm,y=0cm)atseveralverticalpositions(z).Thetwoz=32cmresultsrepresenttwoseparatesetsof10individualscansperformedunderthesameconditions.TheaverageandstandarddeviationsfortheairkermaateachverticalpositionareprovidedinTable7.3. Themeasurementsofairkermaprovidedgoodreproducibilityateachlocation.Aslightvariationofairkermawasobservedasafunctionofz.Theairkermaaver- Page101 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel TABLE7.3AirKermaMeasuredAlongtheCentralAxis(x=0cm,y=0cm)fortheAS&ESmartCheckatTransportationSecurityAdministration’sSystemsIntegrationFacility VerticalPosition-z(cm) AirKermaperScan(nGy) StandardDeviation(nGy) 32 113 4 32 113 4 120 108 5 150 105 4 202 111 3 aged110nGyperscanandwasobservedtobeafewpercenthigherattheupperandlowerregionsofthescan.Becausethesystemutilizesafixed,horizontallyorientedtubegeometrythatistranslatedvertically(thereisnotubeangulation),itwouldbeexpectedthattheairkermashouldbenearlyconstantalongtheverticalextentofthescan.Thesmallvariationsofairkermaobservedmayresultfromthetimerequiredfortubeaccelerationanddecelerationatthebeginningandendofthescan,respectively.Uncertaintyintheabsolutevalueoftheairkermaisalsosubjecttouncertaintyinthechambercalibration.Comparisonsamongvariouschambercalibrationsperformedona50kVbeam(2.08mmHVL)performedattheUniversityofFloridaindicatesthattheuncertaintyinthe150ccchambercalibrationperformedfortheL60beamshouldbelessthan4percentdifferentfromthespectralresponseofthis50kVbeam. Bystander(OutsidetheScreeningVolume) LeakageRadiationGeometry Thelowlevelsofradiationencounteredduringthebystandersetofmeasurementsrequiredcontinuousintegrationoveraperiodof4-5minutes.TheFluke451Bwasoperatedinintegrationmodeandneverrecordedanyvaluesabove0nGy.ResultspresentedarebasedontheKeithleymodel96020C150ccionchamberwithchargecollectedbythePTWUnidoseelectrometer.Atlowexposurelevels,thebackgroundandelectrometer/chamberleakagecanproduceasignificantcontributiontothemeasuredresult.Inordertoreducethiscontribution,abaselinemeasureofbackgroundelectrometer/chamberleakageratewasmade.Anestimateofthistotalcontributionwasmadebasedontheresultingintegrationtimeandsubtractedfromthegrosschargeaccumulatedovertheperiod.Thenetaccumulatedchargewassubsequentlyconvertedtoairkermausingtheappropriatechambercalibrationfactorandmakingairtemperatureandpressurecorrectionsrelativetothechamber’scalibrationconditions.Theintegratedresultswerethendivided Page102 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel TABLE7.4AirKermaperScanOutsidetheInspectionAreafortheAS&ESmartCheck Position AirKermaperScan(nGy) StandardDeviation(nGy) Leakage—Rearexterior 0.23 0.83 x=−100cm,y=0cm,z=150cm Scatter—Centerofexit 1.7 0.45 x=0cm,y=−66cm,z=120cm Scatter—Operatorsideofexit 2.8 0.25 x=−27cm,y=−66cm,z=120cm bythenumberofscansincludedforeachmeasurementpositiontoprovidetheaverageairkermaperscanateachmeasurementposition,illustratedinTable7.4. Standarddeviationisrelativelylargeattheverylowexposurelevelsforeachofthesemeasurements.Thestandarddeviationobservedbetweenmultiplesetsofmeasurementsaveragearound0.5nGyperscan.Consequently,thereportedvaluesoftheleakageradiationaresolowastobestatisticallyindistinguishablefromthebackgroundradiation.ThisshouldnotbesurprisingbecausetheXraysproducedbya50kVbeamarereadilyattenuatedbyquitemodestthicknessesofleadthatmaybeexpectedtobeincorporatedintothescanningsystem. ScatterRadiationGeometry Measurementofthescatterradiationfieldswasperformedataveryconservativeposition(theveryedgeoftheAITsystem)andproducedsmallbutmeasurableradiationexposures.ThereportedvaluessuggestthattheremaybeslightlymorescatterintensityinthedirectiontowardtheX-raysource.Thismaybeexpectedbecauseagreatersurfaceareaofthephantomisavailabletoscatterintothisdirection,andthegenerationofscatterwithinthephantomisexpectedtobemostlyisotropicattheseenergies.Measurementswerethusnotmadeattheoperatorposition,onlyattheedgeoftheAITsystem.Itshouldalsobenotedthattheoperatorpositioncanbealteredfromside-to-side(i.e.,itcanbelocatedoneithertheentranceortheexitside)onthissystem,butitisconfinedtothesidehousingtheanteriorX-raysource.Radiationfieldsareexpectedtobesymmetricalinthe+/–ydirectionsbasedonthesystemgeometryandmeasurementsperformedonapreviousgenerationAS&EAITsystembyNIST. Page103 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel CommitteeReviewoftheAS&ESmartCheckSystemDesign ThecommitteedidnothavethesamelevelofaccesstotheAS&EsystemthatithadtotheRapiscanSecure1000systematNIST.ThisdifferenceinaccessisduetotheAS&EsystembeingsubjectedtoTSAqualificationteststhatimposerestrictionsonhowitcanbehandled,butanAS&Erepresentativepointedoutanddescribedthevariousinterlocksandsafetyfeatures.Fromthesedescriptions,thecommitteedevelopedasummaryofthecommittee’sfindings,giveninTable7.5.AswiththeRapiscanSecure1000installedatNIST,thecommitteewasabletoconfirmthattheAS&EAITsysteminstalledatTSIFmetthesame6of14requirementsforallradiation-emittingdevicesinANSI/HPSN43.17(Section7.2.1)andthesame5ofthe6requirementsforgeneral-useradiation-emittingdevices(Section7.2.2).Anadditional3requirements(Sections7.2.1jandl,and7.2.2e)couldnotbeconfirmedbecausetheoperationalAITsystemcannotbeforcedtoperformtheaction.Theinterlocks,safety,andcontrolrequirementsinANSI/HPSN43.17-2009thatcouldbeverifiedfortheAITsystemarelistedinBox7.1. KeyFinding:Basedonthecommittee’sinspectionoftheAS&ESmartChecksystemwiththeAS&Erepresentativepresent,thecommitteewasunabletoidentifyanycircumstanceswhereanaccidentalfailureordeliberatereconfigurationoftheAITsystemcouldresultineitherapersonbeingscreenedortheoperatorreceivingalargerX-raydosethanthenormalscreeningdose. Becausethereisnofailuremechanismthatwouldgivemorethananormalscreeningdose,asstatedinthekeyfinding,scanningtimeistheonlyfactorleft.TheAITsystemwouldhavetooperateformorethan16hourstoexceedthedoselimitof250,000nSv,asstatedinTable7.5(row7.2.1m);itisunreasonabletoexpectthatapersonbeingscannedwouldbeexposedforthatamountoftime. THERAPISCANSECURE1000SYSTEMMEASUREMENTRESULTSANDSYSTEMDESIGN ARapiscanSecure1000(serialnumberS51023005)becameavailableformeasurementsinJuly2014.ThisAITsystemhadbeeninserviceatLaGuardiaAirportandwaslatertransferredtoNIST,whereitwasinstalledandcalibratedbythemanufacturer’stechnicians.ThisAITsystemcanthusprovideinformationindicativeoftheperformanceoftheAITsystemsthatwereinstalledpreviouslyinairports.ForthepurposesofthemeasurementsdonebytheNRCsubcontractors,thesoftwareusedbyTSAandNISTwereidentical.Duringsomemeasurements,theengineeringmodewasusedtocontrolscanmotion. Page104 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel TABLE7.5SummaryoftheCommittee’sReviewoftheAS&ESmartCheckComparedtotheRequirementsinSections7.2.1and7.2.2ofANSI/HPSN43.17-2009 Text CommitteeComments ANSI/HPSSection7.2.1 a.Thereshallbeatleastoneindicator,clearlyvisiblefromanylocationfromwhichascancanbeinitiated,thatindicateswhenascanisinprogress. ConfirmedonNISTAITsystem. b.Thereshallbeatleastonelightedindicatorclearlyvisiblefromtheinspectionzone.Forportalsystemstheindicatorshallbevisiblefromanyapproachtotheinspectionzonetoindicatethatascanisinprogress. ConfirmedonNISTAITsystem. c.Powertothesystemshallbecontrolledbyakeyswitch.Thekeyshallbecaptured(unabletoberemoved)wheneveritisinapositionthatallowsexposurestobeinitiated. ConfirmedonNISTAITsystem. d.Eachsystemshallhaveameansfortheoperatortoinitiatetheemissionofradiationotherthanthefunctionofaninterlockorthemainpowercontrol. Operatorinitiatesscanfromcomputerconsole.ConfirmedonNISTAITsystem. e.Eachsystemshallhaveameansfortheoperatortoterminatetheemissionofradiationotherthanthefunctionofaninterlock. “Stopscan”iconincludedoncomputerscreen.ConfirmedonNISTAITsystem. f.Meansshallbeprovidedtoensurethatoperatorshaveaclearviewofthescanningarea. Operationalrequirementthatissitespecific.NotconfirmedonNISTAITsystem. g.AgroundfaultshallnotresultinthegenerationofXraysoractivateascanbeamfromasealedradioactivesource. Committeeunabletoconfirmimpactofagroundfault. h.Failureofanysinglecomponentofthesystemshallnotcausefailureofmorethanonesafetyinterlock. Committeeunabletodeterminetheimpactofcomponentfailure. i.Atoolorkeyshallberequiredtoopenorremoveaccesspanels.Accesspanelsshallhaveatleastonesafetyinterlock. ConfirmedonNISTAITsystem. j.Forstationary-subjectsystems,thescanningmotionoftheX-raybeamrelativetothesubjectshallbeinterlockedandtheexposureshallterminatewhentherateofmotionofthebeaminanydirectionfallsbelowapresetminimumspeed. Notconfirmed.Committeebelievesimagequalitywouldpreventoperationintheseconditionswhenadvancedimagingtechnologyisnotused. k.Forportalsystems,theminimumwalkingordrivingvelocitythroughtheinspectionzoneshallbedeterminedbythemanufacturer. NotapplicabletostationarysubjectAITsystems. l.Operationalinterlocksshallterminatetheprimarybeamintheeventofanysystemproblemthatcouldresultinabnormalorunintendedradiationemission. Notconfirmed.Committeebelievesincreasedradiationexposurewoulddistortimageorcausedailytesttofail. m.Intheeventofamalfunction,thesystemshallterminateradiationexposurerapidlyenoughsothatnolocationonthesubject’sbodyshallreceiveanambientdoseequivalent(H*10)exceeding250µSv(250,000nSv),regardlessofthesizeoftheexposedarea. InthisreportitisshownthatforanormalscanthecomputedeffectivedosesareaboutanorderofmagnitudelowerthantherecommendedANSIstandardof250nSv/screen.Comparingthe6secondscanand~25nSv/screenversusa250,000nSvlimit,theexposurewouldhavetolastformorethan16hours. Page105 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Text CommitteeComments n.FollowinginterruptionofX-rayproductionorexternalgammaemissionbythefunctioningofanysafetyinterlock,resettingtheinterlockshallnotresultintheproductionofXraysoremissionofgammaradiation. ConfirmedonAS&EprototypeAITsystematTSIF.   ANSI/HPSSection7.2.2 a.ForanyX-raysystemthatnormallykeepshighvoltageappliedtotheX-raytubeattimesotherthanduringascan,thereshallbeatleastonelighted“Xrayon”indicatoratthecontrolconsolewhereXraysareinitiatedindicatingwhenXraysarebeingproduced. ConfirmedonAS&EprototypeAITsystematTSIF. b.Techniquefactorsforeachmodeofoperationshallbepresetbythemanufacturerandshallnotbealterablebythesystemoperator. ConfirmedonAS&EprototypeAITsystemthattechniquefactorscannotbechangedwhenAITsystemisinoperatormode.VerifiedindiscussionwithTSA. c.EachaccesspaneltotheX-raysourceshallhaveatleastonesafetyinterlocktoterminatetheX-rayproductionwhenopened. ConfirmedonAS&EprototypeAITsystematTSIF. d.ThefollowingwarninglabelshallbepermanentlyaffixedorinscribedontheX-raysystematthelocationofanycontrolsusedtoinitiateX-raygeneration:“CAUTION:X-RAYSPRODUCEDWHENENERGIZED.” ConfirmedonAS&EprototypeAITsystematTSIF. e.X-rayemissionshallautomaticallyterminateafterapresettimeorexposure. Notconfirmed.CommitteebelievesthisverificationispartofthequalificationtestingunderwayatTSIF. f.Forportalsystems,motionsensorsshallmonitorthespeedofpedestriansorvehiclesthroughtheinspectionzone(intheforwarddirection)andtheradiationexposureshallterminatewhenthespeeddropsbelowtheminimum(asdeterminedaccordingtoSection7.2.1k). NotapplicabletostationarysubjectAITsystems. Half-ValueLayerResults Inordertostoptheverticalscanmotion,thepowertotheverticalpositioningmotorwasturnedoffandtheX-rayheadwasmanuallymovedtothedesiredheightandclampedinplace.Inthisposition,thetopofthetubehousingwashorizontal,atapproximatelyz=85cm.TheengineeringsoftwarewasutilizedtooverrideinterlocksandallowX-rayproductioninthisconfiguration.OneAITsystemunitwasturnedoffwhilemeasurementsweremadefortheotherone.TheresultsforboththeanteriorandtheposteriorunitareshowninTable7.6andFigures7.5,7.6, Page106 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel BOX7.1 ANSI/HPSN43.17-2009RequirementsVerifiedfortheAS&ESmartCheck 7.2Indicators,Controls,andSafetyInterlocks 7.2.1RequirementsforAllSystems:Therequirementsofthissubsectionapplytoallthesystemsregardlessofcategoryortypeofradiationsource.Inadditiontotheserequirementssystemsmustcomplywiththerequirementsofoneofthesections7.2.2through7.2.5asappropriate. a.Thereshallbeatleastoneindicator,clearlyvisiblefromanylocationfromwhichascancanbeinitiated,thatindicateswhenascanisinprogress. b.Thereshallbeatleastonelightedindicatorclearlyvisiblefromtheinspectionzone.Forportalsystemstheindicatorshallbevisiblefromanyapproachtotheinspectionzonetoindicatethatascanisinprogress. c.Powertothesystemshallbecontrolledbyakeyswitch.Thekeyshallbecaptured(unabletoberemoved)wheneveritisinapositionthatallowsexposurestobeinitiated.Turningonthekeyswitchshallneverresultintheexternalemissionofradiation. i.Atoolorkeyshallberequiredtoopenorremoveaccesspanels.Accesspanelsshallhaveatleastonesafetyinterlock. j.Forstationary-subjectsystems,thescanningmotionoftheX-raybeamrelativetothesubjectshallbeinterlockedandtheexposureshallterminatewhentherateofmotionofthebeaminanydirectionfallsbelowapresetminimumspeed.Theminimumspeedshallbechosensothatthedoseduringtheexposureperiodiswithintheapplicablelimit. l.Operationalinterlocksshallterminatetheprimarybeamintheeventofanysystemproblemthatcouldresultinabnormalorunintendedradiationemission.Thisshallinclude,butisnotlimitedto,unintendedstoppageofbeammotion,abnormalorunintendedX-raysourceoutput,computersafetysystemmalfunction,terminationmalfunction,andshutterorbeamstopmechanismmalfunction. m.Intheeventofamalfunction,thesystemshallterminateradiationexposurerapidlyenoughsothatnolocationonthesubject’sbodyshallreceiveanambientdoseequivalent(H*10)exceeding250,000nSv(25mrem),regardlessofthesizeoftheexposedarea. 7.2.2RequirementsforGeneral-useSystemsUsingX-raySources:InadditiontotherequirementsofSection7.2.1,“RequirementsforAllSystems,”thefollowingrequirementsapplytogeneral-usesystemsusingX-raysources: c.EachaccesspaneltotheX-raysourceshallhaveatleastonesafetyinterlocktoterminatetheX-rayproductionwhenopened. d.ThefollowingwarninglabelshallbepermanentlyaffixedorinscribedontheX-raysystematthelocationofanycontrolsusedtoinitiateX-raygeneration:“CAUTION:X-RAYSPRODUCEDWHENENERGIZED.” e.X-rayemissionshallautomaticallyterminateafterapresettimeorexposure. SOURCE:TheANSI/HPSN43.17-2009standard,“RadiationSafetyforPersonnelSecurityScreeningSystemsUsingX-RayorGammaRadiation,”isavailableattheHealthPhysicsSocietywebsiteathttp://hps.org/hpssc/index.html. Page107 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel TABLE7.6RapiscanSecure1000Half-ValueLayerMeasurementResults Aluminum Thickness(mm) Normalized Exposure AnteriorUnit Uncertainty AnteriorUnit Normalized Exposure PosteriorUnit Uncertainty PosteriorUnit 0.0 1.00 0.005 1.00 0.007 0.05 0.95 0.008 0.94 0.003 0.1 0.90 0.005 0.89 0.004 0.15 0.86 0.018 0.84 0.004 0.2 0.83 0.003 0.81 0.003 0.25 0.79 0.012 0.77 0.004 0.3 0.76 0.005 0.75 0.000 0.35 0.73 0.009 0.71 0.005 0.4 0.71 0.002 0.68 0.008 0.45 0.68 0.004 0.65 0.002 0.5 0.65 0.006 0.63 0.003 0.55 0.63 0.003 0.60 0.003 0.6 0.61 0.007 0.58 0.002 0.65 0.59 0.003 0.56 0.003 0.7 0.58 0.004 0.56 0.005 0.8 0.55 0.010 0.52 0.002 0.9 0.51 0.004 0.48 0.003 1.0 0.48 0.007 0.46 0.005 1.1 0.45 0.000 0.43 0.002 1.2 0.44 0.003 0.42 0.000 1.3 0.41 0.002 0.39 0.000 1.4 0.40 0.002 0.37 0.004 1.5 0.37 0.007 0.35 0.002 2.0 0.30 0.003 0.28 0.000 2.5 0.24 0.002 0.22 0.004 3.0 0.20 0.003 0.19 0.005 3.5 0.17 0.000 0.16 0.003 4.0 0.15 0.004 0.13 0.002 4.5 0.13 0.006 0.12 0.002 5.0 0.11 0.003 0.10 0.003 NOTE:Eachmeasurementresultshownistheaverageofatleastthreemeasurementscans.Theuncertaintyrepresentstheobservedstandarddeviationinthereplicatemeasurementsforeachaluminumthickness. and7.7.Eachmeasurementistheaverageofatleastthreemeasurementscans,asmeasuredincoulombs,andthennormalizedtothevalueatzeroaluminumthickness.HVL1andHVL2were0.92and1.47mmAlfortheanteriorunitand0.85and1.42mmAlfortheposteriorunit,respectively. PercentDepthDoseResults DepthdosemeasurementswereatthesameheightastheHVLmeasurements,z=85cm,withx=0cmandy=0cm.TheresultsaretabulatedinTable7.7andshowninFigures7.6and7.7. Page108 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel FIGURE7.5NormalizedexposureasafunctionofaluminumthicknessfortheRapiscanSecure1000for(a)theanteriorunitand(b)theposteriorunit.Errorbarsarenotshownsincetheyareapproximatelythesizeoforsmallerthanthesymbols. Page109 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel FIGURE7.6Percentdepthdose(PDD)fortheRapiscanSecure1000anteriorunitcollectedusingthePS-033thin-window(0.5mg/cm2)ionchamberattissuethicknesses(a)upto6mmand(b)lessthan10mm. Page110 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel FIGURE7.7Percentdepthdose(PDD)fortheRapiscanSecure1000posteriorunitcollectedusingthePS-033thin-window(0.5mg/cm2)ionchamberattissuethicknesses(a)upto6mmand(b)lessthan10mm. Page111 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel TABLE7.7PercentDepthDose(PDD)fortheRapiscanSecure1000AnteriorandPosteriorUnitsforDataCollectedonthePS-0330.5mg/cm2and32mg/cm2WindowChambers TissueDepth (mm) Anterior Posterior PDD(%) 0.5mg/cm2 chamber PDD(%) 32mg/cm2 chamber PDD(%) 0.5mg/cm2 chamber PDD(%) 32mg/cm2 chamber   0.00   98.98 100.00 100.00 100.00   0.02 100.00       —   96.19       —   0.20   96.87   98.17   96.77   97.96   0.34   98.36   97.47   98.62   97.69   0.51   98.30   96.76   94.77   96.48   0.71   96.70   94.49   90.92   95.49   0.99 102.36   92.43   85.79   93.32   2.03   91.69   86.74   81.72   86.25   3.12   88.31   81.47   75.16   80.43   4.24   80.39   76.56   73.94   74.37   5.87   78.45   68.58   69.50   66.98   7.95   66.29   58.45   57.93   59.68   9.65   55.12   56.29   56.99   54.78   15.55   37.99   40.96   36.06   41.12   20.35   34.52   32.58   31.95   31.96   26.25   25.40   24.97   24.38   25.34   31.05   22.23   20.36   20.57   18.68   40.70   14.82   14.15   10.81   12.91   51.40   13.03     9.79     9.65     8.96   62.20     5.67     7.59     9.65     6.45 PDDdatawerecollectedusingthelarger15ccparallel-plateionchamber(32mg/cm2windowthickness).Thelargersensitivevolumeofthischamberprovidedimprovedsignalcollectionatthelowexposuresproducedbythescanningsystem.AcomparisonoftheresponseforthesetwochambersisreportedinFigure7.8.Thecomparisondemonstratesthatconsistentdatawerecollectedfrombothchambersexceptatverysmallvaluesfortissuedepthwherethedosepeakobservedusingthethin-window(0.5mg/cm2)4.9cm3chamberwasoverwhelmedbythethicker(32mg/cm2)windowofthe15ccchamber. Standarddeviationsforeachsetofexposuremeasurementswerecalculatedbasedonthereplicatedatasetandweretypicallyabout3percentofthemeanvalue,withthelargestbeing5.7percentforthethin-windowchamber.Forthe15ccchamber,thestandarddeviationforeachsetofexposuremeasurementsaveragedlessthan1percentofthemeanvalue,withthelargestbeing1.5percent.Uncertaintiesinthetissuedeptharesubstantiallysmallerthanthesizeofthesymbolsintheaccompanyingfigures. Page112 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel FIGURE7.8Comparisonofpercentdepthdose(PDD)datafortheRapiscanSecure1000collectedusingthethin-window(0.5mg/cm2)chamber(triangles)andthe32mg/cm2windowchamber(circles)for(a)theanteriorunitand(b)theposteriorunit. Page113 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel AirKermaResults PersonBeingScreened Airkermawasmeasuredwiththe150ccparallel-plateionchambercenteredatmultipleverticallocations(seeTable7.8)forboththeanteriorandtheposteriorunit.Themeasurementlocationswereselectedtoevaluateanyvariationsinbeamintensityasthebeamscansvertically.Becauseofthelowintensityofthescanningbeam,aseriesof10individualmeasurementswererecordedandaveragedtoprovidetheairkermaateachverticallocation. Twoadditionalsetsofmeasurementsweremadeatpositionsx=25.8cm,y=0cm,z=82.8cm,andx=−25.8cm,y=0cm,z=82.8cm,whichspecifylocations30cmfromthefrontsurfaceoftheanteriorandposteriorunits,respectively.ThisprovidedareferenceairkermathatmaybeusedtodemonstratecompliancewiththeapplicableANSIstandardandisalsoidentifiedinTable7.8. Aseriesof10individualmeasurementsweremadeateachmeasurementlocation.Eachmeasurementwasmadewiththeionchamberpositionedaspreviouslydescribed,andanormal,butsingle-sided,subjectscanwasperformed.TheaverageandstandarddeviationfortheairkermaateachverticalpositionareprovidedinTable7.8. TABLE7.8AirKermaMeasuredAlongtheCentralAxis(x=0cm,y=0cm)atSeveralVerticalPositions(z)fortheRapiscanSecure1000 VerticalPositionz(cm) AnteriorUnit PosteriorUnit AirKerma perScan (nGy) Standard Deviation (nGy) AirKerma perScan (nGy) Standard Deviation (nGy)   26.8 27 2 26 2   48.8 28 2 31 1   82.8 29 2 32 2 122.8 31 2 30 2 138.8 28 2 30 2 161.8 27 2 30 2 184.8 26 1 29 2 184.8 — — 29 2 194.8 — — 33 1 At30cmfromx-surface   82.8 48 3 56 4 NOTE:Thetwoz=184.8cmresultsrepresenttwoseparatesetsof10individualscansperformedunderthesameconditions. Page114 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Bystander(OutsidetheScreeningVolume) LeakageRadiationGeometry Ameasurementlocationonthebacksideoftheposteriorunitwasselectedtoevaluateleakageradiationthatmaybeexitingtheunit.The150ccparallel-plateionchamberwaspositionedagainsttherearexterioroftheposteriorAITsystemassemblyataheightofz=171cm,withx=−130cm,andy=0cm,centeredonthepaththattheX-raysourcetravelswhileverticallyscanning. ScatterRadiationGeometry Inordertorepresentthegeometrythatwouldcauseradiationtobescatteredoutsideofthesubjectscanningareatowardbystanders(e.g.,passengersnotbeingscreenedandtransportationsecurityofficers),ananthropomorphicphantomrepresentativeofanadultmalewasusedasdescribedpreviously. Results Thelowlevelsofradiationthatwereexpectedtoresultfromthissetofmeasurementsrequiredcontinuousintegrationoveraperiodofapproximately2minutes.TheFluke451Bwasoperatedinintegrationmodeandneverrecordedanyvaluesabove0nGy.ResultspresentedarebasedontheKeithleymodel96020C150ccparallel-plateionchamberwiththechargecollectedbythePTWUnidoseelectrometer.Atlowexposurelevels,thebackgroundandelectrometer/chamberleakagecanproduceasignificantcontributiontothemeasuredresult.Inordertoreducethiscontribution,abaselinemeasureofbackgroundelectrometer/chamberleakageratewasmade.Anestimateofthistotalcontributionwasmadebasedontheresultingintegrationtimeandsubtractedfromthegrosschargeaccumulatedovertheperiod.Thenetaccumulatedchargewassubsequentlyconvertedtoairkermausingtheappropriatechambercalibrationfactorandmakingairtemperatureandpressurecorrectionsrelativetothechamber’scalibrationconditions.Theintegratedresultswerethendividedbythenumberofscansincludedforeachmeasurementpositiontoprovidetheaverageairkermaperscanateachmeasurementposition,illustratedinTable7.9. CommitteeReviewoftheRapiscanSecure1000SystemDesign ThecommitteedidnothaveaccesstoRapiscanpersonnelorAITsystemdesigndocumentationduringthecourseofthisevaluationbecauseRapiscancouldnotparticipatewithinthesettimeframeofthestudy,butthecommitteedidreview Page115 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel TABLE7.9AirKermaperScanOutsidetheInspectionAreaoftheRapiscanSecure1000 Position AirKermaperScan(nGy) StandardDeviation(nGy) Leakage—Rearexterior 4.0 6.0 x=130cm,y=0cm,z=171cm Scatter—Centerofexit 0.0 16 x=0cm,y=72cm,z=120cm Scatter—Operatorsideofexit 7.0 4.0 x=−44.8cm,y=72cm,z=120cm thepublicdocumentationavailable,frombothpublicsourcesandTSA,fortheRapiscanSecure1000.ThecommitteealsoinspectedtheRapiscanSecure1000AITsystemthatwasmadeavailabletothecommitteeatNIST. Afewoftheinterlocks,safety,andcontrolrequirementsintheANSIstandardcouldnotbeverifiedinthefieldorwithoutreviewingthemachinedesignorfullydisassemblingamachine.However,thecommitteeassumesthattheRapiscanSecure1000machinedesignandinterlockswere(asrequired)demonstratedbythevendortomeetANSI/HPSN43.17-2009ortheversionofANSI/HPSN43.17inforceatthetimeofqualificationtestingatTSApriortodeploymentatairports. DocumentationforCompliancewithANSIStandards Thefactoryacceptancetest(FAT)andthesiteacceptancetest(SAT)andotheroperatingproceduresdefinetheprocedurespriortodeploymentandafterinstallationofanybackscattersystem.ThedocumentsusedbyTSAandequipmentproducersinpreviousyears,duringdeploymentoftheRapiscanbackscatterAITsystemsatairports,referstoFormR-0646,“RadiationEmissionMeasurementforSecure1000.”Thisform,andtheaccompanyingFormR-0685,defineswhatisinspectedandmeasuredfromaradiation-safetyperspectiveduringFATandSATandinthefollowingsituations: Aftersystemrelocation, Duringmaintenance,and Annually. FormsR-0646andR-0685forallfieldedAITsystemshavebeenpubliclyavailableontheTSAwebsiteforseveralyears,16buttheyarecurrentlyunavailable _______________ 16TransportationSecurityAdministration,“SurveysofBackscatterImagingTechnologyMachines,”http://www.tsa.gov/research-center/surveys-backscatter-imaging-technology-machines,accessedJuly23,2014. Page116 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel online;onlyalistofdocumentsisprovidedonthewebsite.17Theformsrequestthefollowinginformationpertinenttoradiationsafety: X-raytubeserialnumber(anteriorandposteriorunit); Theresultofanemergencystopbuttontest; Ifscaninprogresslightswereoperational; IfX-raycautionlabelswerepresentontheanterior,posterior,andcommunicationsunits; IfX-raywarninglabelswerepresentontheX-raygeneratorsfortheanteriorandposterior; Theoutcomeofasafetyinterlocktest; Ifthekeyisremovablewhentheunitisinoperation; Settingsofthegenerator(voltageandcurrent); Lengthofthescantime,inseconds; Iftheoperatorinstructionsareavailable;and GeneralconditionoftheAITsystem. Itisnotspecifiedwhattheexactsafetyinterlocktestreferredtoaboveis.ThecommitteenotesthefollowingpointsrelatedtoexistinginterlocksystemsastheyaredescribedintheRapiscanoperatormanual: Powertothesystemiscontrolledbyakeyswitch.Thekeyswitchhasthreepositions“off,”“standby,”and“on.”Whenthekeyisplacedon“standby,”thesystemwaitsforcommandsfromtheoperatorconsoleandwilltimeoutifcommandsarenotreceived. Amechanicalsensoratthebottomofthedoorisdepressedwhenthedoorisclosed.Ifthedoorisopened,thesensorisreleasedandtheinterlockpreventsoperationofthesystem.Bothanteriorandposterioraccess-panelinterlocksmustbeenabledforascantoinitiateandcomplete. X-rayswillterminateifthereisovervoltageorovercurrent. Referencedetectorsignal.WhenadetectorisplacedintheX-raybeam,theX-rayintensityismonitoredforradiationlevelsoutofrange. Velocityofverticalmotion.AsensorthattravelswiththeX-raytubewillgenerateelectricalimpulsestomonitorverticalmotion.X-raysareterminatedifmotionstops. Velocityofhorizontalmotionofthescannedbeam.Anopticalinterruptsensorlocatedontheassemblyisusedtomonitorthattherotationalvelocityismaintained.X-raysareterminatedifspeedisoutoftolerancelimits. _______________ 17ThelinkstothedocumentspostedonApril11,2013,May24,2011,andMarch16,2011,nolongerwork. Page117 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel X-raytubeheadtemperature.X-rayswillterminateiftheX-raytubeisoutofrange. Safety-relatedinformationthatwasrequestedbyFormR-0646includedthefollowing: Testprocedureused(describedbelow), Backgroundradiationreading, Measurementinstrumenttype(andserialnumber),and Dataacquired. Theformindicatedthatdataacquiredshouldincludemeasurementsofwhereapersonwouldstandwhenbeingscreened—calledinbeamradiationexposuremeasurements—whichconsistoftotalintegratedexposureasaveragedover10measurementsusingaFluke451Pmeterpositioned304.8mm(12inches)fromthecenterofthescanwindowand914.4mm(36inches)fromthefloorofbothanteriorandposteriorunits.18Dataacquiredshouldalsoincluderadiationleakagemeasurements,whicharesimilartoinbeammeasurementsbutlocatedatfourpositionsatthecenteroftheactiveunits’externalsurface,forboththeanteriorandtheposterior,whereapotentialbystandercouldbe.Thefinaldataacquiredshouldincludeinspectionzoneboundaryradiationdosemeasurements,done304.8mm(12inches)fromtheedgesoftheunitsscanwindows(fourmeasurements),againwhereapotentialbystandercouldbe. ThedataonFormsR-0646andR-0685werecomparedtotheexposurelimitsset,andifresultswerewithintheadministrativeintegratedexposurelimits,theAITsystemwasconsideredtomeettheANSI/HPSN43.17-2009standardwithrespecttolimitsforreferenceeffectivedoseandX-rayleakage.Ifanyvalueexceededthelimits,thatfactwouldbereportedtoserviceprogrammanagerspriortoplacingasystemintooperation. KeyFinding:Acceptancetestsandperiodicinspectiontestsguidedbythesafetyinspectionformspreviouslyusedduringdeploymentaresufficientto _______________ 18TheModel451PIonChamberSurveyMeterisahand-held,8atmpressurized,230ccactivevolumeairionizationchambermeterdesignedtomeasuregammaandX-rayradiationabove25keVandbetaradiationabove1MeV.Theplasticchamberwallis200mg/cm2thick.Theinstrumenthasa±10percentaccuracyofreadingbetween10and100percentoffull-scaleindicationonanyrange.Thetypicalrelativeenergyresponseisapproximately0.4for20keV,0.8for40keV,and1for50keV(FlukeBiomedical,“451PPressurizedµradIonChamberRadiationSurveyMeter,”http://www.flukebiomedical.com/biomedical/usen/radiation-safety/Survey-Meters/451P-pressurized-ionchamber-radiation-detector-survey-meter.htm?PID=54793,accessedJuly23,2014). Page118 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel meettheindicators,controls,andsafetyinterlocksrequirementsoftheANSI/HPSN43.17-2009. SafetyProceduresforMaintainingtheRapiscanSecure1000DuringtheCourseofItsUse AccordingtothewrittensafetyproceduresfortheRapiscanSecure1000,priortoanystartupofaunit,thereshouldbeverificationthatserviceaccessdoorsforeachAITsystemmoduleareclosedandlockedbeforepoweringuptheAITsystemmodules.Inordertoensurethatthesystemisworkingproperly,personnelshouldrunascanatleastonceadayandinspecttheimageofatestpiecetoensurethatneededsafetysystemswereworkingproperly.Onamonthlybasis,thereshouldbeinspectionofallexternalcablesforpossiblewearordamageaswellasinspectionofthe“ScaninProgress”lighttoensurethatallwordsareilluminated.Onasemiannualbasis,thereshouldbeinspectionofthefunctionalityoftheX-raypowersupply,thecontroller,andtheinternalcontrolcomputer,aswellasforallwarninglightbulbs. Theequipmentwastobeservicedonlybyqualifiedandtrainedserviceproviders.Operatorsoftheequipmentwerenottoopenanycabinets.Theultimateresponsibilityfortheradiationsafetyofthesystem,theoperators,andthegeneralpublicrestswiththeowner,19whichdesignatedindividualsresponsibleforensuringcompliancewiththerequirementsofANSI/HPSN43.17-2009.Theownerwasalsoresponsibleforensuringapersonneltrainingprogram,withrefreshertrainingprovidedatleastonceevery12months. KeyFinding:EquipmentmanufacturersrecommendthatatestpiecebescanneddailytoevaluateproperoperationoftheAITsystembecausethisensuresthatmanyoftheneededsafetysystemrequirementsinANSI/HPSN43.17-2009workproperly.ThecommitteeagreeswiththisrecommendationbutwasunabletodetermineifthiswasbeingdonebecauseofthecurrentlackofX-raybackscatterAITsinthefieldatcommercialairports. CommitteeReviewoftheInterlocksontheRapiscanSecure1000System ThecommitteeconsideredpotentialfailuremechanismsthatcouldresultinX-rayoverexposureofthepersonbeingscreenedorbystanderssuchastheoperator.OntheRapiscanSecure1000locatedatNIST,committeemembersverifiedthattheX-raysourcecanbeactivatedonlywiththekeyinthe“on”positionwithascaninitiatedandthatthekeycannotberemovedunlessitisinthe“off”position. _______________ 19Inthiscase,theownerwouldbeTSA. Page119 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel ThecommitteeconfirmedthattheX-raysourceturnsoffattheendofeachscan.ScanscouldnotbeinitiatedifanyofthepaneldoorsenclosingtheX-raysourceandotherelectronicswereajaroriftheemergency-offbuttonhadbeenactivated.ThecommitteeverifiedthattheX-raysourceturnedoffimmediatelyeventhoughtheverticalmechanicalscanbarcompletedfulltraveltotheparkpositionatthetoporbottomoftheAITsystem.Theseinvestigationsarelisted,togetherwithpreviousstudies’findings,inTables6.5and6.6inChapter6forcomparisontootherresearchers’resultsandalsogiveninTable7.10. Thesubcontractor’smeasurementsrequiredthattheverticalscanbarbelockedataspecificheight.Toenablethisconfiguration,theAITsystemwasputintoengineeringmode,whichrequiresahigher-levelpasswordthanthatusedforscreeningbutgivesgreateraccesstocontrollingindividualfunctions.Thisway,theverticalscanmotorwasturnedoffandthescanbarwasmovedbyhand.Table7.10summarizesthecommittee’sreviewcomparedtoANSI/HPSN43.17-2009,Section7.2,“Indicators,Controls,andSafetyInterlocks.” ThecommitteewasabletoconfirmthattheRapiscanSecure1000AITsysteminstalledatNISTmet6ofthe14ANSI/HPSN43.17-2009,Section7.2.1requirementsforallradiation-emittingdevicesand5ofthe6ANSI/HPSN43.17-2009,Section7.2.2requirementsforgeneral-useradiation-emittingdevices.Onerequirement(7.2.1f)issitespecificandcouldnotbeverifiedoutsideofobservinganAITsysteminoperationinanairport,andtwooftherequirements(7.2.1g,h)couldnotbeconfirmedbecausetheywouldrequirethedeliberateactivationofapotentiallydestructivefault,whichNISTwouldnotallow.Requirements7.2.1kand7.2.2fdonotapplytoportalsthatrequirethesubjectbeingscreenedtobestationary,suchastheRapiscanSecure1000.Anadditionalthreerequirements(7.2.1j,land7.2.2e)couldnotbeconfirmedbecausetheoperationalAITsystemcannotbeforcedtoperformtheaction,butthecommitteebelievesthatthesefaultsinthefieldwoulddistorttheimagetotheextentthatthescreenercouldnotmakeapass/faildeterminationforthatscreening,andthescreeningwouldnotresultinoverexposureofthepersonbeingscreened.OncetheAITsystemsuseautomaticthreatrecognition,theoperatorswillnotseetheimage,andthischeckwouldnolongerapply. Requirement7.2.1mstatesthatnomalfunctionoftheAITsystemshallresultinanexposureexceeding250,000nSv.ThecommitteecouldidentifynofailuremechanismthatwouldresultinanincreaseintheX-rayphotonemissionfromtheX-raysource(e.g.,increasingtheX-raytubevoltageorcurrent)sothatscanningtimeistheonlymalfunctionthatcouldresultinX-rayexposureexceedingtheANSIstandard.Inthisreport,thecommitteeshowsthatforastandardscreeningofapproximately6seconds,thecomputedeffectivedosesareaboutanorderofmagnitudelowerthantherecommendedANSIstandardof250nSv/screen.ThepersonbeingscreenedwouldhavetostandintheAITsystemwiththeX-raysource Page120 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel TABLE7.10SummaryoftheCommittee’sReviewoftheRapiscanSecure1000ComparedtotheRequirementsinSections7.2.1and7.2.2ofANSI/HPSN43.17-2009 Text CommitteeComments ANSI/HPSSection7.2.1 a.Thereshallbeatleastoneindicator,clearlyvisiblefromanylocationfromwhichascancanbeinitiated,thatindicateswhenascanisinprogress. ConfirmedonAS&EprototypeAITsystematTSIF. b.Thereshallbeatleastonelightedindicatorclearlyvisiblefromtheinspectionzone.Forportalsystemstheindicatorshallbevisiblefromanyapproachtotheinspectionzonetoindicatethatascanisinprogress. ConfirmedonAS&EprototypeAITsystematTSIF. c.Powertothesystemshallbecontrolledbyakeyswitch.Thekeyshallbecaptured(unabletoberemoved)wheneveritisinapositionthatallowsexposurestobeinitiated. ConfirmedonAS&EprototypeAITsystematTSIF. d.Eachsystemshallhaveameansfortheoperatortoinitiatetheemissionofradiationotherthanthefunctionofaninterlockorthemainpowercontrol. Operatorinitiatesscanfromcomputerconsole.ObservedonAS&Eprototype. e.Eachsystemshallhaveameansfortheoperatortoterminatetheemissionofradiationotherthanthefunctionofaninterlock. “Stopscan”iconincludedoncomputerscreen.ConfirmedonAS&EprototypeAITsystematTSIF. f.Meansshallbeprovidedtoensurethatoperatorshaveaclearviewofthescanningarea. Operationalrequirementthatissitespecific.NotconfirmedonAS&EprototypeAITsystematTSIF. g.AgroundfaultshallnotresultinthegenerationofXraysoractivateascanbeamfromasealedradioactivesource. Committeeunabletoconfirmimpactofagroundfault. h.Failureofanysinglecomponentofthesystemshallnotcausefailureofmorethanonesafetyinterlock. Committeeunabletodeterminetheimpactofcomponentfailure. i.Atoolorkeyshallberequiredtoopenorremoveaccesspanels.Accesspanelsshallhaveatleastonesafetyinterlock. ConfirmedonAS&EprototypeAITsystematTSIF. j.Forstationary-subjectsystems,thescanningmotionoftheX-raybeamrelativetothesubjectshallbeinterlockedandtheexposureshallterminatewhentherateofmotionofthebeaminanydirectionfallsbelowapresetminimumspeed. Notconfirmed.CommitteebelievesthisverificationispartofthequalificationtestingunderwayatTSIF. k.Forportalsystems,theminimumwalkingordrivingvelocitythroughtheinspectionzoneshallbedeterminedbythemanufacturer. NotapplicabletostationarysubjectAITsystems. l.Operationalinterlocksshallterminatetheprimarybeamintheeventofanysystemproblemthatcouldresultinabnormalorunintendedradiationemission. Notconfirmed.CommitteebelievesthisverificationispartofthequalificationtestingunderwayatTSIF. Page121 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Text CommitteeComments m.Intheeventofamalfunction,thesystemshallterminateradiationexposurerapidlyenoughsothatnolocationonthesubject’sbodyshallreceiveanambientdoseequivalent(H*10)exceeding250µSv(250,000nSv),regardlessofthesizeoftheexposedarea. InthisreportitisshownthatthecomputedeffectivedosesforanormalscanareaboutanorderofmagnitudelowerthantherecommendedANSIstandardof250nSv/screen.Comparingthe6secondscanand~25nSv/screenversusa250,000nSvlimit,theexposurewouldhavetolastformorethan16hours. n.FollowinginterruptionofX-rayproductionorexternalgammaemissionbythefunctioningofanysafetyinterlock,resettingtheinterlockshallnotresultintheproductionofXraysoremissionofgammaradiation. ConfirmedonNISTAITsystem.   ANSI/HPSSection7.2.2 a.ForanyX-raysystemthatnormallykeepshighvoltageappliedtotheX-raytubeattimesotherthanduringascan,thereshallbeatleastonelighted“Xrayon”indicatoratthecontrolconsolewhereXraysareinitiatedindicatingwhenXraysarebeingproduced. ConfirmedonNISTAITsystem. b.Techniquefactorsforeachmodeofoperationshallbepresetbythemanufacturerandshallnotbealterablebythesystemoperator. ConfirmedonNISTAITsystemthattechniquefactorscannotbechangedwhenAITsystemisinoperatormode.VerifiedindiscussionwithTSA. c.EachaccesspaneltotheXraysourceshallhaveatleastonesafetyinterlocktoterminatetheX-rayproductionwhenopened. ConfirmedonNISTAITsystem. d.ThefollowingwarninglabelshallbepermanentlyaffixedorinscribedontheX-raysystematthelocationofanycontrolsusedtoinitiateX-raygeneration:“CAUTION:X-RAYSPRODUCEDWHENENERGIZED.” ConfirmedonNISTAITsystem. e.X-rayemissionshallautomaticallyterminateafterapresettimeorexposure. Notconfirmed.Assumedtohavebeendemonstratedatthetimeofqualification. f.Forportalsystems,motionsensorsshallmonitorthespeedofpedestriansorvehiclesthroughtheinspectionzone(intheforwarddirection)andtheradiationexposureshallterminatewhenthespeeddropsbelowtheminimum(asdeterminedaccordingtoSection7.2.1k). NotapplicabletostationarysubjectAITsystems. Page122 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel operatingforapproximately10,000timeslongerthanasinglescan(16hours)toapproachthelimitsetinSection7.2.1m,anobviouslylongtime.ThecommitteeconsidersthisrequirementtobemetbecausetheX-raysourceisnotcapableofproducingahigherX-rayenergyorflux,andthetimeapersonwouldhavetostandintheAITsystemtoreceivesuchadoseisunrealisticallylong. TheoverallcommitteeassessmentisthattheRapiscanSecure1000asdesignedmeetstherequirementsofANSI/HPSN43.17-2009. KeyFinding:Basedonthecommittee’sreviewandtestoftheRapiscanSecure1000’sinterlocks,thecommitteewasunabletoidentifyanycircumstanceswhereanaccidentalfailureoradeliberatereconfigurationoftheAITsystemcouldresultineitherapersonbeingscreenedortheoperatorreceivinganeffectivedoselargerthanthatfromanormalscreening. Becausethereisnofailuremechanismthatwouldgivemorethananormalscreeningdose,asstatedinthekeyfinding,scanningtimeistheonlyfactorleft.TheAITsystemwouldhavetooperateformorethan16hourstoexceedthedoselimitof250,000nSvasstatedinTable7.10(row7.2.1m);itisunreasonabletoexpectthatapersonbeingscannedwouldbeexposedforthatamountoftime. Inaddition,itisworthmentioningthattheAITsysteminspectedatNISTcannotbereconfiguredremotelybecauseitisnotconnected,norcanitbeconnected,totheInternetorbymodemtoanyotherdevice.ReconfigurationcanonlybedonefromtheAITsystemitself. SUMMARYOFKEYFINDINGSFORBOTHMEASUREDSYSTEMS ThekeyparametersfortheRapiscanSecure1000andtheAS&ESmartChecksystemstobeusedinthedosecomputationsaresummarizedinTable7.11. TABLE7.11SummaryMeasurementResultsfortheRapiscanSecure1000andtheAS&ESmartCheck HVL1 (mmAl) HVL2 (mmAl) 50PDD (mm) AirKerma (nGy) EREF (nSv) Rapiscananterior 0.92 1.47 ~11 30.6 3.5 Rapiscanposterior 0.85 1.42 ~11 29.8 3.2 AS&E 1.1 1.7 ~12.5 113 15.5 NOTE:EREF,referenceeffectivedose;HVL1,firsthalf-valuelayer;HVL2,secondhalf-valuelayer;PDD,percentdepthdose. Page123 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel DOSECOMPUTATIONS Objectives ThechargetothecommitteeincludedthetaskofdeterminingifradiationexposuresreceivedduringX-raybackscatterAITscreeningwereincompliancewithapplicablehealthandsafetystandardsforthegeneralpublicandoccupationallyexposedindividuals.Itisclearfrompreviousreports(reviewedinChapter6)andthemeasurementsthattheNRCsubcontractormade(seeearlierinthischapter),togetherwiththecomputationsbelow,thattheAITsystemsevaluatedmeettheANSIrequirementforEREFbelow250nSvperscreening.However,ithasbeenspeculatedinrecentyearsthatitmightbepossibleforsomeindividualstoreceiveaneffectivedose,E,duringascreeningthatexceedstheEREFbyalargeenoughmargintoresultinexposuresexceedingANSIrecommendations.Therefore,oneoftheeffortswiththisindependentstudywastogobeyondpreviousevaluations(seestudiesdescribedinChapter6)toincludeanassessmentofabsorbeddoseandeffectivedoseforadults,children,andpregnantwomenunderroutinescreeningconditionsaswellasdosesthatmightbereceivedasaresultofseriousmalfunctions. Introduction TheNRCsubcontractorWesleyBolch,AdvancedLaboratoryforRadiationDosimetryStudies,J.CraytonPruittFamilyDepartmentofBiomedicalEngineering,UniversityofFlorida,appliedstate-of-the-artcomputationaltechniquestoassesstheorgan-absorbeddoseandwhole-bodyeffectivedosereceivedbyadults,children,andthedevelopingfetusofpregnantfemalesscannedbyacomputationallymodeledX-raybackscatterAITsystemandbyvariationsonthatsystemthatincludesomecurrentandanticipatedengineeringdesigns.Passengersweresimulatedusingasuiteofhybriddigitizedphantoms.ThecomputationalphantomsusedinthisstudywereobtainedfromtheUniversityofFloridacomputationalhybridphantomlibrary.20,21ThephantomsareconstructedasacollectionofmathematicalsurfacesbasedinNURBS(non-uniformrationalbasisspline)thatdefinetheshapesandlocationsofindividualinternalorgansaswellasthebodysurfacecontour.Fromthislibrary,eachphantomwasadjustedusingtargetedvaluesforsittingheight(i.e.,basedonthelengthofthetorso,neck,andhead)andfourbodycircumferences: _______________ 20A.M.Geyer,S.O’Reilly,C.Lee,D.J.Long,andW.E.Bolch,TheUF/NCIfamilyofhybridcomputationalphantomsrepresentingthecurrentUSpopulationofmaleandfemalechildren,adolescents,andadults—ApplicationstoCTdosimetry,PhysicsinMedicineandBiology59(18):5225-5242,2014. 21M.R.Maynard,N.S.Long,N.S.Moawad,R.Y.Shifrin,A.Geyer,G.Fong,andW.E.Bolch,TheUFfamilyofhybridphantomsofthepregnantfemaleforcomputationalradiationdosimetry,PhysicsinMedicineandBiology59:4325-4343,2014. Page124 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel waist,buttocks,arm,andthigh.HumanmorphometricdatawereobtainedfromtheNationalHealthandNutritionExaminationSurveydatabase,fromdatacollectedbetween1999and2006.Thephantomlibrarycoversthe5thto95thheightandweightpercentilesforchildrenandadolescents(age2to20)andadults(age20to85)intheUnitedStates. Thisfamilyofhybridcomputationalphantomswasbasedonasetofreferencephantomsrepresentingages1,5,10,and15andadultmalesandfemales.Thesereferencephantomshaveheights,weights,andmassesforinternalorgansdescribedinInternationalCommissiononRadiologicalProtection(ICRP)Publication89.22Scalingwasthenperformedtoeitherincreaseordecreasethetorsoheighttogetherwiththevolumes,andhencethemass,ofallinternalorgans.Thefinalstagewastoaddorsubtractsubcutaneousfattocreatephantomsofdifferentweights,thusforminganarrayofphantomsofdifferingheightandweightcombinations.Theassignedbodymassindex(BMI)foreachphantomisnotuniquebecauseanumberofdifferentcombinationsofheight/weightcanyieldanequivalentvalueofBMI.Thisprocessforphantomlibrarycreationdoesnotincludethepossibilitythatagivenphantomwillhaveitsassignedweightbasedonincreasesordecreasesinskeletalmuscleorleanbodymass.Theimplicitassumptionisthatweightchangesatagivenphantomheightaredictatedbyproportionalchangesinsubcutaneousfat.ItdoesnotimplythatthesephantomsrepresenttheonlyortruemorphologyforthatvalueofBMIforallairlinepassengers. Thesecomputationswerenotdesignedtoestimateradiationexposuretospecificindividuals.Themethodologywasdevelopedtoprovideestimatesofradiationdosesreceivedbyapopulationofpassengerswitharangeofmorphologiesduringroutinescreening.Thiswascomplimentedwithaseriesofsensitivitystudiestoinvestigateadditionalvariations.Thecombinationoftheseapproachesprovidesinformationontheglobaluncertaintiesinherentinthecomputationalapproach. Thecommitteechosetouseagenericmathematicalmodel(orreferencemodel)ofanX-raybackscatterAITsystemratherthananexactmodelofanexistingsystem.Theideaisthatwithsuchamodelsystemitispossibletocomparehowdifferencesindesignandsettingsaffectdosefornotonlyprevioussystemsbutalsopotentialfuturesystems.Thus,aMonteCarlosimulationmodelofareferenceX-raybackscatterAITsystemwasimplementedforthecomputations.Thisreferencesystemwasbasedonacompilationofinformationassembledfromthefollowingsources: _______________ 22InternationalCommissiononRadiologicalProtection,BasicAnatomicalandPhysiologicalDataforUseinRadiologicalProtectionReferenceValues,ICRPPublication89,AnnalsoftheICRP32(3-4),2002. Page125 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Previousreportsdocumentingapproximatescanninggeometry,includingverticaltransportoftheX-raysource,beamsizeanddivergence,andpolarangleofthebeamasafunctionofelevation; Previousreportsdocumentinginformationonbeamintensity(i.e.,airkerma)asafunctionofverticalandhorizontalpositionoftheX-raybeam; DataacquiredbythecommitteefrommeasurementsofHVLinaluminum; DataacquiredbythecommitteefrommeasurementsofPDDintissue-equivalentmaterial;and Theabilitytohavejustananteriororbothananteriorandaposteriorsystem. ThesimulatedX-raybackscatterAITsystemisareferencesystemcomposedofinformationavailabletothecommitteeatthetimeitconducteditsinvestigation.ThenatureofthisMonteCarloapproachissuchthattheresultscanbescaledtoanysystemwithsimilargeometryandphotonenergydistributionbymultiplyingtheratiooftheairkermafromanyotherAITsystemtotheairkermaoftheAITreferencesystem. Threepopulationsofairpassengersweresimulatedasfollows: Referenceadultmalesandfemalesat50thpercentileheightandatfivedifferentweightpercentiles; Children(maleandfemale)at~105cmheightandatthreedifferentweightpercentiles;and Thedevelopingfetusofpregnantfemalesatthreeperiodsofgestation. Inadditiontoroutineorstandardizedscanningoperations,thefollowingsensitivitystudieswereperformedtoevaluatevariationsthatmightaffectcompliancewiththeradiationprotectionstandards: Theeffectofvariationsintheirradiationgeometryofthereferencesystemandthepresumptionofasimplifiedbroadparallelbeamofthesameenergydistribution23onorganandeffectivedose; Theeffectofvariationsinorganandeffectivedoseduetochangesinthehorizontallocationofthescreenedpassengerbetweentheanteriorandposteriorunits; _______________ 23ThisstudywasconductedtoenableevaluationofandcomparisonstoAITsystemsthatmaynotincludeangularvariationsintheverticalandhorizontalscan,whichiscreatedbytiltingtheX-raysourceasitmovesfromthebottomtothetopofthescanningregionandfixedhorizontalpositionofthetubeanode.ThestudyalsointendstodocomparisonswithpreviouscomputationsthatmadetheparallelbeamassumptionduetomodelinglimitationsoftheirMonteCarloapproach. Page126 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel AssessmentofbothorganandeffectivedoseasafunctionofX-raytubepotentialgreaterthanthenominal50kV; Assessmentoftheradiationabsorbeddoseaveragedacrosstheentireskinofanadultpassenger(bothdermisandepidermis)duringonescreenascomparedtotheassociatedradiationdosetotheradiosensitiveregionofskinatadepthof50to100µmfromtheskinsurface,alsoaveragedacrossthetotalbody;and Assessmentoftheradiationabsorbeddoseperscreentotheadultfemalebreastandlensoftheeyeandacentralregionoftheskinduringapresumedworst-casemalfunctionwherethehorizontalandverticalsweepremainedstationaryforthesamedurationasthatofanormalscan. X-RaySourceTerm FeaturesoftheReferenceAITSystem TodevelopthemathematicalmodelofthereferenceAITsystem,somefeaturesreportedbyNISTwereadopted,including(1)therelativegeometricalconfigurationsoftheanteriorandposteriorscanningunitsandtheirX-raytubes;(2)therelativevaluesofhorizontalandverticalairkermawithinthescanningregion;and(3)themeasuredairkermaperscanatareferencepoint(usedtonormalizetheMonteCarloorgandoses).Thegeometryofthescanningunitsisdiscussedinalatersection.Items2and3wereincorporateddirectlyintotheconstructionoftheX-raysourcetermusedtoirradiatethecomputationalphantomsduringvirtualscreeningsimulations. Thehorizontal(paralleltoAITsystemface)andverticalexposuremaps,showninFigures7.9and7.10,providedanapproximatemeasureoftherelativephotonfluenceataplanelocatedafixeddistancefromtheanteriorandposteriorunits.Thefiguresarenormalizedto1.0atthelocationinthetwo-dimensionalplanehavingthemaximumvalueofairkerma(i.e.,ataverticaldistanceof192cmfromthemat).ThesedistributionsofrelativeexposurewereimplementedforthereferenceAITsystemandformedthebasisforparticlesamplingfunctionsusedinthevirtualX-raysourcetermforboththeanteriorandtheposteriorunit. TheresultsoftheMonteCarloprocessareinitiallynormalizedtotheabsorbeddoseperincidentphoton.24Theobjectiveistoobtaintheeffectivedoseperscan,whichinturnrequiresthenumberofincidentphotonsperscan.This“normaliza- _______________ 24BecauseMonteCarlocalculationsfollowthehistoriesofindividualphotonsandaveragetheresultsoverlargenumbersofphotons,theresultistheenergydeposited(orabsorbeddose)perphoton.Theabsorbeddoseataspecifiedlocationresultingfromexposuretoaspecificnumberofphotonsisthesumoftheabsorbeddosesatthatspecifiedlocationproducedbyeachoftheprotons. Page127 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel FIGURE7.9Horizontalexposurevariationoftheposteriorunitmeasuredataheightof100cmfromthematatadistanceof30cmfromthefrontplaneoftheAITsystem(red,upwardscan;black,downwardscan).Themaximumexposurefromtheposteriorunitwasmeasuredataverticalpositionof192cmandahorizontalpositionof0cm.SOURCE:Figure10fromNISTReporttoDHS,AssessmentoftheRapiscanSecure1000SinglePose(ATRversion)forConformancewithNationalRadiologicalSafetyStandards,JackL.Glover,RonaldoMinniti,LawrenceT.Hudson,andNicholasPaulter,NationalInstituteofStandardsandTechnology,Gaithersburg,Md.,finalreportrelatedtoIAANo.HSHQDC-11-X-00585,April19,2012. FIGURE7.10Verticalexposurevariationoftheposteriorunitalongthecentralaxisofthepersonbeingscannedatadistanceof30cmfromthefrontplaneoftheAITsystem.Thegreatestexposureisseentowardthetopofthescan.Thedownwardscan(black)showsamaximumataheightof192cm.Theupwardscan(red)showsitsmaximumataheightof188cm.SOURCE:Figure11fromNISTReporttoDHS,AssessmentoftheRapiscanSecure1000SinglePose(ATRversion)forConformancewithNationalRadiologicalSafetyStandards,JackL.Glover,RonaldoMinniti,LawrenceT.Hudson,andNicholasPaulter,NationalInstituteofStandardsandTechnology,Gaithersburg,Md.,finalreportrelatedtoIAANo.HSHQDC11-X-00585,April19,2012. Page128 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel tionfactor”isobtainedfromtheratioofmeasuredairkermaperscantotheMonteCarlo-simulatedvalueofairkermaperphoton.Thisyieldsthenumberofphotonsperscan.Theresultspresentedinthefollowingsectionsarenormalizedtoavalueof9.203×108photonsperscan,whichcorrespondstoanairkermaof68nGy/scanrepresentingasimulatedscanningprotocolforthereferenceAITsystem.Allresultsrelatingtoorganabsorbeddoseandeffectivedosesreceivedduringpassengerscreeningwillscalelinearlywiththevalueofairkerma. PhotonEnergyDistributionUsingHVLandPDD TheenergyspectrumoftheincidentphotonsisamajorcomponentoftheinputtotheMonteCarlocalculations.TheMATLAB-basedcodeSPEKTR,25basedonthemethodspresentedbyTurneretal.,26wasusedtogenerateacandidatespectrum.Itgeneratesacandidate“soft”clinicalX-rayspectrumbasedonenteringthehigh(peak)voltage,inkilovolts(kV),andhigh-voltageripple.27Typically,theuserthen“hardens”thecandidatespectrumbycalculatingtheeffectoffilteringthespectrumwithaselectedabsorbingmaterial(e.g.,aluminum)untiltheresultingHVLsofthismodifiedspectrummatchthemeasuredvalues.ThisprocessyieldstherepresentativespectrumemergingfromthatX-raytubeandinherentfiltration. ThefirstavailabledatafromtheNRCsubcontractoryieldedanHVL(HVL1)of1.18mmAlobtainedfrommeasurementsofanAS&ESmartCheckAITsystem.However,thecandidatespectrumusing50kVgeneratedbySPEKTRhadanHVL1valueofapproximately1.45mmAl.Thecandidatespectrumwastherefore“softened”byiterativelyaddinglow-energyphotonsusinganinverseprocessofexponentialattenuationasafunctionofphotonenergy.TheeventualresultwasasuitablysoftenedspectrumwithanHVL1matchingthatinitiallymeasuredfortheAS&ESmartCheck.Figure7.11visuallycomparestheoriginalcandidatespectrumandthesoftenedspectrummatchingtheAS&ESmartCheckHVL1valuesinitiallymeasured.28 _______________ 25J.H.Siewerdsen,A.M.Waese,D.J.Moseley,S.Richard,andD.A.Jaffray,Spektr:Acomputationaltoolforx-rayspectralanalysisandimagingsystemoptimization,MedicalPhysics31:3057-3067,2004. 26A.C.Turner,D.Zhang,H.J.Kim,J.J.DeMarco,C.H.Cagnon,E.Angel,D.D.Cody,D.M.Stevens,A.N.Primak,C.H.McCollough,andM.F.McNitt-Gray,AmethodtogenerateequivalentenergyspectraandfiltrationmodelsbasedonmeasurementformultidetectorCTMonteCarlodosimetrysimulations,MedicalPhysics36:2154-64,2009. 27Powersuppliesoftodayhaveverylittleripple,andthusthevoltageisclosetoconstantandthepeakvalue(Vp)isthesameastheaveragevalue;inthiscase,itisenoughtoreportthevoltage(V)insteadofVpandtheripple. 28Theinitialmeasurementswereusedfordesigningthegenericcomputationmodelfordosecalculations;later,themeasurementswererefinedandarereflectedinthereportedvaluesofTable7.11. Page129 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel FIGURE7.11ComparisonoftheinitialcalculatedX-rayspectrumat50kVyieldingafirsthalf-valuelayer(HVL1)of1.45mmofaluminum(mmAl)andtherevisedsoftenedspectrumthatyieldsanHVL1of1.18mmAl.SOURCE:TomBorak. EnergySampling ThesoftenedenergyspectrumshowninFigure7.11wasincorporatedintothecomputationalX-raysourceterm.StandardMonteCarlomethodsbasedonrandomnumberswereusedtosamplephotonenergiesfortheemergingscanningbeamwithprobabilitiesrepresentedbythisdistribution. SimulatingtheScanningX-RayBeamSpotIncidentUponthePassenger TheobjectivesofthisprocessarebothtoreproducetheintensityoftheX-raybeamatlocationsinthey-zreferenceplaneandtoincludethedirectionorvectorofthebeamasitinterceptsthepassenger.Thisdependsonthetiltangleofthebeamduringverticaltranslationandonthelateralangleofthebeamspotasitscanshorizontally. Page130 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel VerticalandHorizontalIntensitiesofScanningBeam ThebasisforsamplingtheoriginanddirectionofthephotonsusedfortheX-raysourcetermofthereferenceAITsystemaregiveninFigures7.9and7.10.ThesoftwarePlotReaderTMwasusedtomanuallycapturedatapointsfromeachfigure.NISTreportedrelativeexposuresinthereferenceplaneforbothupwardanddownwardscanningmotions.Upwardanddownwardexposuredatawereaveragedateachpointforeachfigure.Thehorizontaldata(Figure7.9)werethenfittedpiece-wisetotwoGaussianfunctionsandthennormalized.Theverticaldata(Figure7.10)weredigitizedinto1cmbinsusinglinearinterpolationinMATLABTMandthennormalized.Thehorizontalandverticaldatasetsnowrepresentedtherelativedistributionofphotons(asafunctionofyandz)thatshouldbeexpectedatareferenceplanelocated30cmfromandparalleltothefrontplaneofascanningunit.Theserelativedistributionswereassumedforboththeanteriorandtheposteriorunit.AnimplicitassumptioninthisworkisthatthisX-rayenergydistributionwasconstantacrossallhorizontalanglesofthebeamsweep. PhotonStartingPositionandDirection RandomlysamplingthetwoprobabilitydistributionsrepresentingFigures7.9and7.10describedaboveprovidesthelocationofaphotonincidentuponareferenceplanelocated30cmfromthefrontofascanningunit.Thestartingpositionofthephotonwasdeterminedbylinearlymapping(raytracing29)backtowardthegeometriclocationoftheX-raysourceinthereferenceAITsystem,accountingforadditionalspecificationssuchasverticaltranslationandtiltangleofthesourceassociatedwiththatverticalposition.Theraytraceprovidesaunitvectorcorrespondingtothedirectionoftheemittedphoton. NormalizationtoAirKerma AllresultsprovidedbytheMCNPXcodewerenormalizedtothenumberofstartingsourcephotons.ThenumberofstartingsourcephotonsmustbescaledbythetotalnumberofX-rayphotonsperscantoyielddosesinabsoluteunits.Theusermust,therefore,post-processresultswithsomephysicalquantity(orquantities)toprovideananchoringbetweensimulatedandphysicaldosequantities.Allresultsfromascansimulationobtainedinthismannermustbemultipliedbya“normalizationfactor”toconvert,forexample,fromdose-to-passengerperstartingphotontodose-to-passengerperscan.OncetheX-raysourcetermwasconstructed _______________ 29Raytracingisatechniqueforgeneratinganimagebytracingthepathoflight(orXrays)throughthepixelsinanimageplaneandsimulatingtheeffectsofitsencounterswithvirtualobjectssuchas,inthiscase,thehumanphantomorpartsoftheX-raybackscatterAITsystem. Page131 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel andcompiled,thenormalizationfactorwasestimatedbysimulatingavirtualairkermameasurementanalogoustothatmadewithaphysicalionchamberinanearlierreport(68nGyperscanataknownlocation).30AsphereofairwitharadiusandlocationequivalenttotheRadcalCorporationionchamberusedbyNISTwasmodeledinMCNPXandirradiatedusingthesimulatedX-raysourceterm.TheNISTairkermameasurementwasdividedbytheresultingvirtualairkerma(nGyperstartingphoton),yieldinganestimateofthetotalnumberofphotonsemittedperscan(9.203×108photonsperscaninthisstudy).ItwasnotnecessarytomodelthecomplexgeometryoftheNISTionizationchamberbecausethechamberwascalibratedbyNISTtoprovideanairkermameasurementtoasimilarlysizedvolumeofairaswasmodeledinMCNPX. ValidationofMonteCarloSamplingProcedures TheX-raysourcetermwasvalidatedinthreeways:(1)byconfirmingthatthesimulatedvirtualscansweregeneratingthedesiredphotonenergyfluenceandthusthecorrectHVL;(2)bycomparingsimulatedandanalyticalnormalizationfactors;and(3)bycomparingsimulatedPDDwithmeasuredPDD. Thevirtualfluencevalidationwasachievedusingthereferenceplanelocated30cmawayfromandparalleltothefrontplanedefiningthescanningregionoftheAITsystem.Thesurfacewasdividedinto1-cmbinsalongthehorizontalandverticaldirections.VirtualscanswereperformedusingtheX-raysourceterm,andthephotonfluenceineachofthesurfacebinswasquantifiedandplotted.Asexpected,thephotonfluenceasafunctionofhorizontalandverticaldistance(Figure7.12)mirrorsthecompositeofFigures7.9and7.10,indicatingthatthedistributionofphotonsproducedbythesimulatedreferenceAITsystemisverysimilartothatproducedbytheRapiscanSecure1000AITsystemtestedatNIST. ThenormalizationfactorderivedfromMCNPX(9.203×108photonsperscan)wasvalidatedviacomparisontoacalculatednormalizationfactor.UsingtheHVL1matched(1.18mmAl)50kVspectrum,massenergy-absorptioncoefficientsforair(astandardNISTtable31)wereusedtocalculatethenumberofphotonsrequiredtodeliver68nGytoavolumeofairequalinsizetothedetectorusedforairkermameasurements.Additionally,usingMCNPX,thefluenceintothatvolumeofair _______________ 30Thevalueof68nGywasselectedbasedonanearliermeasurementmadebyNISTbecausemeasurementsbytheNRCsubcontractorofairkermaperscanwerenotavailablewhenitwasnecessarytobegintheMonteCarlocomputations.Allresultsrelatingtoorganabsorbeddoseandeffectivedosesreceivedduringpassengerscreeningwillscalelinearlywiththevalueofairkerma.NISThassinceupdateditsreport,and,therefore,68nGyisconsideredagenericvalue. 31P.J.LampertiandM.O’Brien,NISTMeasurementServices,CalibrationofX-RayandGamma-RayMeasuringInstruments,NISTSpecialPublication250-58,April2001,http://www.nist.gov/calibrations/upload/sp250-58.pdf. Page132 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel FIGURE7.12Compositehorizontalandverticalrelativephotonfluenceatplane30cmfromfrontplaneofascanningunitassimulatedinMCNPX.SOURCE:TomBorak. fromonecompletescanwascalculatedtomakethevaluerelativetoonescan.Acalculatedvalue(8.00×108photonsperscan)basedonafirstcollisionapproximationwaswithin15percentofthenormalizationfactorderivedfromMCNPX. ThevalidationusingPDDwasachievedbyvirtuallysimulatingthepertinentirradiationgeometryadoptedbytheNRCsubcontractorduringthephysicalmeasurements.Thebeamwasmodeledsimulatingafullhorizontalscanwitha3mmverticalcollimation.Thevirtualsimulationsincorporatedasofttissuephantomwithdensityandelementalcompositionscomparabletothephysicalphantommaterialusedinthephysicalmeasurements.Thedetailedgeometryoftheparallel-plateionizationchamberdidnotneedtobemodeledinthevirtualsimulationsbecausethesoftwarewasabletoestimatetissueabsorbeddosedirectly.SimulateddoseswerequantifiedasafunctionofdepthinthevirtualtissuephantomandusedtogenerateaPDDcurve.ThesimulatedPDDiscomparedtothemeasuredPDDinFigure7.13. DescriptionofthePassengerIrradiationGeometry AvisualrepresentationoftheirradiationgeometryusedforthereferenceAITsystemisprovidedinFigure7.14.TheNISTcoordinatesystemwasadopted(Figure7.1),wherethex-axisisthedirectionparalleltothefacesofthescanningunits,they-axisisthedirectionorthogonaltothefacesofthescanningunits,andthez-axisistheverticaldirection.ThedistancesbetweentheAITsystem’santeriorandposteriorsurfaces(109cm)andplanes(87cm)wereobtainedfromtheNISTreport.32Thedistancefromtheanteriorplanetothesource(48cm)wasalsoob- _______________ 32Gloveretal.,AssessmentoftheRapiscanSecure1000SinglePose(ATRversion)forConformancewithNationalRadiologicalSafetyStandards,2012. Page133 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel FIGURE7.13Comparisonsbetweenmeasuredandpercentdepthdose(PDD)intissueequivalentmaterial.BluecirclesareresultsfromMCNPradiationtransportsimulation,andorangetrianglesaremeasurementsbytheNRCsubcontractorontheAS&ESmartChecksystem.Resultsareshownwith(a)linearand(b)logarithmicdepthscale.SOURCE:TomBorak. tainedfromthesameNISTreport.Areferencepointof30cmfromtheanteriorplanewasusedintheirradiationgeometry.Thehorizontal(x-axis)scanwidthwasapproximately90cmatthispoint,accordingtomeasurementsdetailedintheNISTreportdiscussedinthissection.BasedonvisualinspectionofaRapiscanSecure1000unitatTSIF,thesourceverticallytraverses(z-axis)approximately118cminonescanandreachesamaximumheightofapproximately152cm.Therotationalangleofthesourceatitsmostverticalpoint(+45degrees)wasobtainedfromtheoriginalpatentapplication.Thisconfigurationyieldsamaximumverticalscanheightofapproximately230cm.Therotationalangleofthesourceatitslowestverticalpointwasestimatedtobe−26degrees. Withtheexceptionofthepassenger-positioning-sensitivitycalculationsdone Page134 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel FIGURE7.14DimensionaldatausedtoestablishtheirradiationgeometryfortheNRCreferenceX-raybackscatterAITsystemusedintheMonteCarloradiationtransportsimulations.SOURCE:ThomasB.BorakandWesleyE.Bolch,UniversityofFlorida. bytheNRCsubcontractor,allphantomswerecenteredasfollows:(1)paralleltothefacesoftheAITsystems(x-axis),facingtheanteriorunit,and(2)betweentheanteriorandposteriorunits(centerofphantomatadistanceof43.5cmfromthefrontplaneoftheAITsystem).Allphantomswerearrangedinarepresentativescanningpositionwitharmsraised(Figure7.15).Itisnotedthatbecausethevirtualpassengerswerecenteredbasedontheiranatomicalextent,thelocationsofthefeetwereslightlydifferentasthesubject’sbodyweightincreasedamongthemodelseries. Page135 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel FIGURE7.15Graphicalimagesofthecomputationalhybridphantom,anadult50thpercentilemale,witharmsraisedandpositionedwithinthescanninglocationbetweentheanteriorandposteriorunits.SOURCE:WesleyE.Bolch,UniversityofFlorida. AdultReferencePhantoms Theadultmalesandfemalesrepresentingthe5th,25th,50th,75th,and95thpercentilesforweightattheirrespective50thpercentileforheightwereutilized.Lateralandanterior-posteriorviewsoftheadultmaleandfemalephantomsthatwereusedinthesesimulationsareshowninFigures7.16and7.17,respectively.Thecoloredfeaturesprovidevisualdistinctionoftissuesandorgans.Grayregionsrepresentvariationsinadditionalfatandsurfaceskin.Thefiguresdonotincludepixilationthatquantitativelydifferentiatesskinandsubcutaneousfat. PediatricPhantoms Pediatricmaleandfemalephantomswerechosenataheightof105cmandcorrespondingto5th,50th,and95thpercentilesforweight.The105cmheightcorrespondstoanapproximateageofa4.5-year-oldchild.Thisheightwasmeanttocorrespondtotheshortestpassengersthatmightbescreened.Lateralandanterior-posteriorviewsofthepediatricmaleandfemalephantomsthatwereusedforthesesimulationsareshowninFigures7.18and7.19,respectively. Page136 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel FIGURE7.16Leftlateral(top)andanterior-posterior(bottom)viewsoftheadultmalephantomsusedforthepassengerscreeningsimulationssetat50thpercentileforheightandvariedbybodymassindex:(A)5thpercentile,(B)25thpercentile,(C)50thpercentile,(D)75thpercentile,and(E)95thpercentile.SOURCE:WesleyE.Bolch,UniversityofFlorida. Page137 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel FIGURE7.17Lateral(top)andanterior-posterior(bottom)viewsoftheadultfemalephantomsusedforthepassengerscreeningsimulationssetat50thpercentileforheightandvariedbybodymassindex:(A)5thpercentile,(B)25thpercentile,(C)50thpercentile,(D)75thpercentile,and(E)95thpercentile.SOURCE:WesleyE.Bolch,UniversityofFlorida. Page138 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel FIGURE7.18Leftlateralandanterior-posteriorviewsofthepediatricmalephantomsusedforscreeningsimulationssetat105-cmheightandvariedbybodymassindex:(A)5thpercentile,(B)50thpercentile,and(C)95thpercentile.SOURCE:WesleyE.Bolch,UniversityofFlorida. FIGURE7.19Leftlateralandanterior-posteriorviewsofthepediatricfemalephantomsusedforscreeningsimulationssetat105-cmheightandvariedbybodymassindex:(A)5thpercentile,(B)50thpercentile,and(C)95thpercentile.SOURCE:WesleyE.Bolch,UniversityofFlorida. Page139 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel PregnantFemalePhantoms Thepregnantfemalephantomseriesprovideshighlydetailedanatomicalrepresentationforeightfetalagesspanninganentirepregnancy.Threeofthesephantoms,representingfetalages(post-conception)of15weeks,25weeks,and38weeks(Figures7.20to7.22),werevirtuallyscreenedinMCNPXtoestimatefetaldosesresultingfromthesimulatedX-raybackscatterAITsystemirradiation. DosimetryResultsforStandardScreeningConditions AllphantomsimulationspresentedinthisreportwereperformedinMCNPXv2.7usingthecustomX-raysourcetermdescribedearlierandthepassengerpositioningdescribedaboveinFigure7.14.AllsimulationswereperformedontheUniversityofFloridaHiPerGatorsupercomputerusingparticlehistoryspecificationsthatyieldedsufficientlylowrelativeerrors(majority<1percent).Anterior FIGURE7.20The15-weekpregnantfemalephantom:afrontalview(A)andmagnifiedright-obliqueview(B).SOURCE:WesleyE.Bolch,UniversityofFlorida. Page140 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel FIGURE7.21The25-weekpregnantfemalephantom:afrontalview(A)andmagnifiedright-obliqueview(B).SOURCE:WesleyE.Bolch,UniversityofFlorida. FIGURE7.22The38-weekpregnantfemalephantom:afrontalview(A)andmagnifiedright-obliqueview(B).SOURCE:WesleyE.Bolch,UniversityofFlorida. Page141 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel FIGURE7.23Diagramshowinghowtheadultmaleandfemalephantomdataarecombinedtoobtainsex-averagedeffectivedoseresultsforadultpassengers.NOTE:Mreferstomale,Freferstofemale,andTreferstoaspecifictissueororgan.SOURCE:TomBorak. andposteriorscansweresimulatedindependentlyandmathematicallysummedtoprovideresultsforatotalpassengerprotocol. Theeffectivedoseisdeterminedbyapplyingtissue-weightingfactorstoallexposedtissuesandorgans.However,theseweightingfactorsrepresentmeanvaluesforhumans,averagedoverbothsexesandallages.InordertofacilitatecomparisonsoftheseresultswiththeANSIlimitofreferenceeffectivedose,thecommitteecombinedtheresultsofthemaleandfemalephantomsusingtheprocessoutlinedinICRPPublication10333(seeFigure7.23). ResultsofthedosimetrycalculationsforadultpassengersareshowninTable7.12(andforpediatricpassengersinTable7.13andforthedevelopingfetusinTable7.14).Theabsorbeddosereceivedperscreentopertinentorgansisshownseparatelyformalesandfemales.CompletelistsofabsorbeddosesforallmaleandfemaleorgansareprovidedinAppendixC.Theeffectivedoseisthevalueobtainedbyaveragingtheresultsfrombothmaleandfemalephantoms. SensitivityAnalysis Severalsensitivityanalyseswereconductedtoexplorepossibledosevariationunderdifferentscreeningscenarios.Theseanalysesincludeirradiationgeometry,passengerposition,skinsensitivity,failuremodes,andX-rayenergyandspectralshape. _______________ 33ICRPPublication103,2007. Page142 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel TABLE7.12SummaryperAITScreeningofCriticalOrganAbsorbedDoseandEffectiveDosetoAdultPassengersof50thHeightPercentileatFiveDifferentWeightPercentiles WeightPercentiles,U.S.Adults 5th 25th 50th 75th 95th Maleabsorbeddoseperscreen(nGy) Thyroid 31 27 24 24 16 Skin 44 43 43 42 42 EyeLens 44 44 42 42 39 Femaleabsorbeddoseperscreen(nGy) Breast 26 23 23 20 18 Thyroid 22 21 17 11 4 Skin 46 45 44 45 46 EyeLens 46 44 43 37 32 EffectiveDose(nSv) Peranteriorscan 12 10 9 7 4 Perposteriorscan 3 3 3 2 2 Perscreen 15 13 12 9 6 NOTE:Forcomparison,theANSIreferenceeffectivedoseforanHVL1of1.18mmAlandanairkermaof68nGyperscanis20nSv. TABLE7.13SummaryperAITScreeningofCriticalOrganAbsorbedDoseandEffectiveDosetoPediatricPassengersof~105cminTotalHeightandThreeDifferentWeightPercentiles WeightPercentiles,U.S.Children 5th 50th 95th Maleabsorbeddoseperscreen(nGy) Thyroid 47 45 47 Skin 49 49 48 EyeLens 60 60 60 Femaleabsorbeddoseperscreen(nGy) Breast 43 39 32 Thyroid 47 44 48 Skin 49 46 48 EyeLens 60 54 60 EffectiveDose(nSv) Peranteriorscan 20 18 16 Perposteriorscan 6 5 5 Perscreen 25 23 22 NOTE:Forcomparison,theANSIreferenceeffectivedoseforanHVL1of1.18mmAlandanairkermaof68nGyperscanis20nSv. Page143 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel TABLE7.14AbsorbedDosesperAITScreeningtotheFetusandFourFetalOrgans,IncurredduringAnteriorScan,PosteriorScan,andTotalScreenfortheU.S.AdultPregnantFemaleat15Weeks,25Weeks,and38WeeksPost-Conception AbsorbedDose(nGy) 15WeeksPost-Conception 25WeeksPost-Conception 38WeeksPost-Conception Anterior Posterior Screen Anterior Posterior Screen Anterior Posterior Screen Wholebody 7.2 1.3 8.5 3.4 0.6 4.0 3.4 0.9 4.3 Brain 3.7 2.3 6.0 0.8 1.4 2.2 0.5 2.7 3.2 Lungs 8.3 0.9 9.2 5.1 0.2 5.3 2.6 0.2 2.7 Thyroid 5.8 1.4 7.2 2.5 0.4 2.9 1.3 0.3 1.6 Activebonemarrow 14 2.5 16 6.4 1.8 8.1 8.4 2.7 11 Page144 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel StandardGeometryversusPlaneParallelBeams Theeffectofbeamgeometryonpassengerdosewasinvestigatedinthisanalysis.Twobeamgeometriesweresimulated:abroad,uniformparallelbeam,andthegeometryoftheNRCreferenceAITsystemdescribedabove.TheuniformparallelbeamwasmodeledusingthesameX-rayspectrum(Figure7.11)andairkerma(68nGyperscan)describedearlier.However,thehorizontalexposureprofileinFigure7.9aswellastheverticalexposureprofileinFigure7.10werereplacedwithuniformdistributions.Thus,thetwo-dimensionalbeamprofileforthereferenceAITsysteminFigure7.12isrepresentedasaflatsurface.Theadultmaleandadultfemalephantoms(50thpercentileheightandweight)werescannedusingeachgeometry,andtheresultingdosesaresummarizedinTable7.15. PassengerPositionWithintheUnit Variationsinthedosetoorgansandeffectivedosereceivedbythepassengerduetopositionvariationsbetweentheanteriorandposteriorunitswasinvestigatedbyplacingtheadultmalephantomcloserandfurtherfromeachscanningunit TABLE7.15AbsorbedDosestoCriticalOrgansforMalesandFemalesandEffectiveDosesfor50thPercentileofU.S.AdultsUsingtheBeamGeometryDevelopedfortheNRCReferenceX-RayBackscatterAITSystemandaPlaneParallelBeamGeometryIncidentUponthePassengers Geometry ReferenceAITScanner UniformParallelBeam Ratio Maleabsorbeddoseperscreen(nGy) Thyroid 24 49 2.0 Skin 43 78 1.8 EyeLens 42 65 1.6 Femaleabsorbeddoseperscreen(nGy) Breast 23 36 1.6 Thyroid 17 40 2.3 Skin 44 80 1.8 EyeLens 43 68 1.6 EffectiveDose(nSv) Peranteriorscan 9 15 1.7 Perposteriorscan 3 4 1.5 Perscreen 12 19 1.7 NOTE:Thethirdcolumnshowstheratiobetweenthesetwogeometries.Forcomparison,theANSIreferenceeffectivedoseforanHVL1of1.18mmAlandanairkermaof68nGyperscreenis20nSv. Page145 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel TABLE7.16ChangesinOrganAbsorbedDoseandEffectiveDoseperScreenwithShiftsTowardtheAnteriorUnitorTowardthePosteriorUnit DistanceAwayfromCenterScanningPosition(cm) TowardAnteriorUnit TowardthePosterior 15 10 5 0a 5 10 15 Maleabsorbeddoseperscreen(nGy) Thyroid 30 28 26 24 22 21 20 Skin 43 43 42 43 43 44 45 EyeLens 53 49 45 42 38 35 33 Femaleabsorbeddoseperscreen(nGy) Breast 30 27 25 23 21 20 18 Thyroid 20 19 18 17 17 16 15 Skin 45 44 44 44 45 46 47 EyeLens 57 51 46 43 40 36 33 Effectivedose(nSv) Peranteriorscan 12 11 10 9 8 8 7 Perposteriorscan 2 2 2 3 3 3 3 Perscreen 14 13 12 12 11 11 11 Ratio(positiontonominal) 1.2 1.1 1.0 1.0 1.0 0.9 0.9 aThezerovaluereferstothenominalandcentralscanningpositionbetweenananteriorandaposteriorunit. NOTE:Forcomparison,theANSIreferenceeffectivedoseforanHVL1of1.18mmAlandanairkermaof68nGyperscreenis20nSv. inincrementsof5cm.Thetotaltranslationaldistancewas30cm(±15cmfromcenter).TheresultingdosesaresummarizedinTable7.16. VariationsinX-RayTubeVoltage Asensitivityanalysiswasperformedtoinvestigatetheeffectsofvaryingbeamvoltageondosestotheadultphantom.Dosesresultingfromthebeamspectrumgeneratedforthisreport(thebeamspectrumusedwasmatchedtotheHVL1measuredbytheNRCsubcontractor)werecomparedtodosesresultingfromadditionalspectraas-generatedfromtheSPEKTRcode34(i.e.,theHVL1softhesespectrawerenotmodifiedbeyondtheirinherentvalues).EachspectrumwasincorporatedintotheAITsystemX-raysourcetermandutilizedtovirtuallyscreentheadultmaleandfemalephantomunderthesameirradiationgeometrydescribedearlier.Table7.17providesasummaryoftheresultingorganabsorbeddosesandeffectivedosereceivedbythepassenger. _______________ 34J.H.Siewerdsen,A.M.Waese,D.J.Moseley,S.Richard,andD.A.Jaffray,Spektr:Acomputationaltoolforx-rayspectralanalysisandimagingsystemoptimization,MedicalPhysics31:3057-3067,2004. Page146 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel TABLE7.17ComparisonofReferenceX-RayBackscatterAITSystemoftheOrganAbsorbedDoseandEffectiveDoseasaFunctionofX-RayTubePotential AbsorbedDose X-RayTubePotential(kV) 50a 50 60 70 80 90 100 Half-valuelayer(HVL1) 1.18 1.45 1.74 2.02 2.30 2.58 2.86 Maleabsorbeddoseperscreen(nGy) Thyroid 24 27 33 37 41 45 48 Skin 43 45 47 50 52 54 55 EyeLens 42 44 45 47 48 50 51 Femaleabsorbeddoseperscreen(nGy) Breast 23 26 29 32 35 37 39 Thyroid 17 22 26 31 35 39 42 Skin 44 46 49 52 54 56 57 EyeLens 43 45 47 49 50 52 53 Effectivedose(nSv) Peranteriorscan 9 11 13 15 17 19 21 Perposteriorscan 3 3 5 6 8 10 11 Perscreen 12 14 18 22 25 29 32 Ratio(tocolumn1) 1.0 1.2 1.4 1.7 1.9 2.2 2.3 ANSIReferenceEffectiveDose 20 25 30 34 39 44 49 aValuesinthefirstdatacolumnareresultsfromthePDDvalidatedandsoftenedX-rayspectrumattheoperationalvalueof50kV.AllothervaluesarefromTASMIP-generatedspectra(withoutHVL1matching)andassuminganequivalentreferenceairkermaof68nGyperscan.http://www.ncbi.nlm.nih.gov/pubmed/9394272. DosetoRadiosensitiveCellsintheSkin Theskinisdividedintotwomainregions:thedermisandtheepidermis.Thebiologicalresponseintheepidermalregionoccurssoonafteranexposuretoionizingradiationwhereasthebiologicalresponseinthedermalregionoccursafteralatentperiodfollowingexposuretoionizingradiation.35Thebiologicaltargetsarebasalcellsintheepidermisandthefibroblasts/vascularendothelialcellsinthedermis.Irradiationofthebasalcelllayercanleadtodesquamation,whileirradiationofthefibroblastsandvascularendothelialcellscanleadtoerythema(skinreddening).TheICRPreferencevalueforthethicknessoftheepidermallayeris70µmforadults.36 _______________ 35E.J.HallandA.J.Giaccia,RadiobiologyfortheRadiologist,LippincottWilliamsandWilkins,Philadelphia,Pa.,2006. 36ICRP,ICRPPublication89:BasicAnatomicalandPhysiologicalDataforUseinRadiologicalProtection:ReferenceValues,AnnalsoftheICRP32,2002. Page147 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Asensitivityanalysiswasperformedtocomparetheradiationdosetotheentireskinthicknesswiththedosetojusttheradiosensitiveepidermalskinlayer.Toconductthisanalysis,astylizedellipticalcylindertorsomodelwascreatedtorepresentthe50thpercentileadultmaleusingthreeanterior-posteriorandthreelateralmeasurementaverages(representingtheupper,middle,andlowerregionsofthetrunk).Thetorsomodelwascomposedofsofttissuecoveredbya0.158cmskinlayer(correspondingtotheassumedstandardICRPskinthicknessofanadultmale). ThemodelwascenteredintheAITsystemanddosestothe0.158cmskindepthregionandthedosetothesensitivearea(50to100µm)skindepthsweresimulated.Theratioofthedoseinthesensitiveregiontothetotalskindosewascalculated.Becausethisratioisnearunity,thedosetotheentireskinthicknesswasconsideredareasonablesurrogatefordosetothesensitivelayer.Usingthisratio,thedosetothesensitiveskinlayeroftheadultmalehybridphantomwasestimatedfromthewholeskindosepresentedearlier.Table7.18summarizestheresults. FailureModeAnalysis Failuremodeanalysisoftwoconditionsofequipmentfailurewasperformedontheadultfemalephantominordertoexaminepossiblemaximumdosestothelensoftheeye,breasttissue,andskin.Thefirstfailuremodeassumedastationaryverticalbeampositionandafunctionalchopperwheelresultinginahorizontallybroadandverticallynarrow(~3mm)beam.Thesecondfailuremodeassumedastationaryverticalbeampositionandanonfunctionalchopperwheelresultinginastationarypencilbeam.Acircularbeamcrosssectionwasassumedforthesecondfailuremodewithanareaequivalenttoa3mm×3mmsquarebeam,theapproximatedimensionsoftheproperlycollimatedscanningbeamundernormal TABLE7.18ComparisonoftheAbsorbedDoseperScantoEithertheTotalSkinVolume(DermisandEpidermis)andthePresumedRadiosensitiveEpidermalStemCellLayer(50to100µm)inaCylindricalStylizedTorsoPhantom AbsorbedDoseperScreen(nGy) StylizedPhantom HybridPhantom Target-Totalskin 37.3 43.5a Target-Radiosensitivelayer 37.9 44.2b Ratio(totalskin/radiosensitivelayer) 1.02 aSex-averageddosewithadulthybridphantoms. bHybridphantomtotalskindose×1.02. NOTE:Thesimulationsshowedonly2percentincreaseindose.Correspondingdosestoskininthe50thpercentileadultmalephantomareshownaswell. Page148 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel TABLE7.19ReferenceGeometryAITAbsorbedDosesUnderConditionsofaStandardScreeningComparedtoThoseIncurredUnderConditionsofMaximumExposureduetoTwoDifferentModesofEquipmentFailure Tissue NormalScreen FailureMode1a FailureMode2b TissueReactionThreshold (nGy) (nGy) (nGy) (nGy) (Gy) Lens 43 29,000 1,100,000 500,000,0000.5 Skin 44 26,000 870,000 2,000,000,0002 Breast 23 310 7,400 aFailureMode1:Beamfixedverticallybutnothorizontally(chopperwheeloperational). bFailureMode2:Beamfixedverticallyandhorizontally(chopperwheelnotoperational). operation.Thebeamsofbothfailuremodeswereorientedtowardthetargetsofinterestandwereassumedtoemitthesamenumberofphotonsproducedundernormaloperationforafullbodyscan.Table7.19summarizestheapproximatedosestothelens,breast,andskinunderthesefailuremodes.Forthesecondfailuremode,peakskindosewascalculatedassuminga1×1cm2areaontherespectiveskinregion.Themaximalskinandlensdoses(failuremode2)of0.87mGy(870µGyor870,000nGy)and1.1mGy(1,100µGyor1,100,000nGy),respectively,arewellbelowtheminimumthresholdvaluesfordeterministiceffectsofbothskin(2Gyor2,000,000,000nGy)37andeyelens(0.5Gyor500,000,000nGy).38Theskindeterminesthethresholdlimitforthebreastduetothesensitivityfornecrosisoftheskincomparedwithclinicalissuesinvolvingbreasttissue.39 Summary TheNRCsubcontractorsandthecommitteeperformedadetailedcomputationalassessmentofthedosesreceivedduringasecurityscreeningprocessinvolvingX-raybackscatterAITsystems.ThisinvolvedadetailedMonteCarlo _______________ 37S.Balter,J.W.Hopewell,D.L.Miller,L.K.Wagner,andM.J.Zelefsky,Fluoroscopicallyguidedinterventionalprocedures:Areviewofradiationeffectsonpatients’skinandhair,Radiology254:326-341,2010. 38F.A.Stewart,A.V.Akleyev,M.Hauer-Jensen,J.H.Hendry,N.J.Kleiman,T.J.MacVittie,B.M.Aleman,A.B.Edgar,K.Mabuchi,C.R.Muirhead,R.E.Shore,andW.H.Wallace,ICRPPublication118:ICRPStatementonTissueReactionsandEarlyandLateEffectsofRadiationinNormalTissuesandOrgans—ThresholdDosesforTissueReactionsinaRadiationProtectionContext,AnnalsoftheICRP41:1-32,2012. 39F.A.MetlerandA.C.Upton,MedicalEffectsofIonizingRadiation,ThirdEdition,Saunders,Elsevier,Philadelphia,Pa.,2008. Page149 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel simulationusingarepresentativesourcetermandstate-of-the-arthybridizedhumanphantoms.ThemodelusedinthecomputationsisreferredtoasthereferenceX-raybackscatterAITsystem.Themodelrepresentsadualscan–single-poseconfigurationwithananteriorunitprovidingananteriorimageandaposteriorunitproducingaposteriorimage.ThespatialdimensionswereobtainedfromthepreviousNISTreportevaluatingaRapiscanSecure1000.ThisalsoincludedthesizeofthecollimatedX-raybeam,verticalspanoftheX-raysource,angularpitchoftheX-raysource,andhorizontalpropertiesofthescannedbeam.TheseresultscanbecomparedwithpreviousstudiesreviewedinChapter6andsummarizedinTable6.4. X-RaySource Typically,theenergydistributionoftheX-rayphotonsincidentonthepersonscannedarederivedfromtheoperatingvoltage,anodeangle,andmeasurementsofthefirstHVL(HVL1)inaluminum.Thisinformationservesasinputtoastandardizedcomputermodelthatyieldedthedesiredenergydistribution.Inthiscase,theinformationcamefromNRCsubcontractormeasurementsmadeonanAS&ESmartCheckandaRapiscanSecure1000AITsystem.Thesemeasurementsalsoincludedacentral-axisPDDintissue-equivalentmaterial.TheobjectivewastousethemeasuredPDDasavalidationoftheMonteCarlosimulationusingthecomputer-generatedenergydistribution. BeamIntensity ThebeamintensityservesasascalefactorforestimatingtheabsorbeddosetothepassengeraswellasacalibrationoftheMonteCarlocomputations.Thequantityusedforthisistheairkermaperscan(innGy)atareferencelocationbetweentheanteriorandposteriorunits.TheMonteCarlomethodtransportsoneincidentphotonatatime.Asimulationoftheairkermameasurementyieldedanormalizationfactorintermsofthenumberofphotonsrequiredtogenerate1nGyofairkerma. Results Inthissection,ascreenisconsideredtobethecombinationofananteriorandaposteriorscanof50kVwithanHVLof1.18mmAlandairkermaof68nGyperscan.Itshouldbenotedthattheresultswillscalelinearlywithairkermaiftheotherconditionsremainthesame. Page150 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Theconventionalmethodforcomputingtheenergydistributionoftheincidentsphotonsfor50kVX-raybackscatterAITsystemsdidnotadequatelypredictthedataobtainedforPDDintissue. Theabsorbeddosestoindividualtissuesandorgansforthereferenceadultphantomslocatedmidwaybetweentheanteriorandtheposteriorwerealllessthan50nGyperscreen. Ingeneral,theabsorbeddosesdecreasedintheadultphantomsastheBMIincreased. Thesex-averagedeffectivedosefortheadultphantomrangedfrom15nSvatthe5thpercentileBMIto6nSvforthe95thpercentileBMI.(TheANSIEREFfortheseconditionsis20nSv.) Thesex-averagedeffectivedosefortheadultphantomwassignificantlygreaterfortheanteriorscancomparedwiththeposteriorscan.ThisdifferenceinallcasesdependsonthedistanceoftheorganfromtheX-raysourceandontheorgan’slocationwithintheindividual. TheabsorbeddosestoindividualtissuesandorgansforthepediatricphantomslocatedmidwaybetweentheanteriorandtheposteriorAITsystemunitswerealllessthanorequalto60nGyperscreen. TheabsorbeddosestotissuesandorgansremainedrelativelyconstantinthepediatricphantomsastheBMIincreased. Thesex-averagedeffectivedoseforthepediatricphantomsrangedfrom25nSvatthe5thpercentileBMIto22nSvforthe95thpercentileBMI.(TheANSIEREFfortheseconditionsis20nSv.) Thesex-averagedeffectivedoseforthepediatricphantomswassignificantlygreaterfortheanteriorscancomparedwiththeposteriorscan. TheabsorbeddosestothefetusofapregnantfemalelocatedmidwaybetweentheanteriorandtheposteriorAITsystemunitswerealllessthan10nGyperscreen. TheabsorbeddosestotheactivebonemarrowofthedevelopingfetusofapregnantfemalelocatedmidwaybetweentheanteriorandtheposteriorAITsystemunitsrangedfrom16nGyat15weekspost-conceptionto11nGyat38weekspost-conception. TheabsorbeddosestoindividualtissuesandorgansforthereferenceadultphantomslocatedmidwaybetweentheanteriorandposteriorAITsystemunitswereallgreaterforaplane-parallelincident-X-raybeamcomparedwiththeexposureconditionsinanactualAITsystem. Thesex-averagedeffectivedosefortheadultphantomsincreasedasthephantomwaslocatedclosertotheanteriorunit. Theabsorbeddosestothelocationsofradiosensitivecells,atdepthsbetween50µmand100µm,werenotsignificantlylargerthanthedoseaveragedoverthecompletelayerofskin. Page151 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Thelocalizedabsorbeddosesforastationarybeaminbothverticalandhorizontaldirectionsandnormalscantimedurationwhilecentereduponthelensofaneye,afemalebreast,orcentralskinofthechestwereontheorderof1,000,000nGyforthelensoftheeyeandtheskinand7,000nGyforthebreast. Foraconstantairkerma,thesex-averagedeffectivedosefortheadultphantomsrangedfrom12nSvatatubevoltageof50kV(HVL=1.18mmAl)to32nSvat100kV(HVL2.86mmAl).TheANSIEREFrangedfrom20nSvto49nSvundertheseconditions. FINDINGSANDRECOMMENDATIONS Measurements KeyFinding:Usingappropriatedetectors,theestimatedvaluesoftheradiationoutsidetheinspectionareathatmightaffectabystanderaresolowastobestatisticallyindistinguishablefromthebackgroundradiation. SystemDesign Althoughtheradiationmeasurementsanddosecomputationswereperformedforthecommitteeinadetailedmanner,thecommitteewasunabletounequivocallydeterminewhethertheX-raybackscatterAITsystemsstudiedhaveadequateoperatingsafetyinterlocksthatwillpreventtheAITsystemfromexceedingtheANSI/HPSN43.17-2009standardundereveryimaginablesituationforthefollowingreasons: Thecommitteewasnotgivenanopportunitytoindependentlyverifyhowalloftheinterlockswouldperformindifferentsituations,withtheexceptionofsimplefunctionssuchasterminationofoperationifadoorwasopened.Suchtestingwouldneedengineeringsupportfromthemanufacturerandrequireuniquetestingtools,anditwouldrequiredismantlingportionsoftheAITsystems,potentiallycausingdamagetothem. ThecommitteewasnotgivenademonstrationofhowinterlocksarecheckedatthemanufacturerlevelfromeitherRapiscanorAS&E. DetailedelectricalandmechanicaldrawingsandcomputercodedescriptionsanddocumentsdescribinginternalfunctionsatthemostfundamentalleveloftheAITsystemsareeitherrestrictedfrompublicaccessorwerenotmadeavailablebythemanufacturerstoeitherthecommitteeorthesponsor. Page152 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel However,thecommitteewasabletoinspecttheinteriorofboththeRapiscanSecure1000andtheAS&EAITsystem.AS&Erepresentativesalsodescribedtothecommitteehowmanyoftheinterlocksareintendedtoperformontheirsecond-generationprototype. Withtheabovelimitationsnoted,havingevaluatedasmanyaspectsoftheAITsystemsasmechanicallyandelectricallyaspossible,andcombiningthatknowledgewiththemeasurementsandcomputationsperformed,thecommitteecanmakethefollowingstatements: KeyFinding:ItappearsthattheX-raybackscattersystemsadheretotherecommendedsafetymechanismsdescribedintheANSI/HPSN43.17-2009standard. KeyFinding:GiventheresultsobtainedbythecommitteeonradiationmeasurementsandcalculationsfortheX-rayAITsystemsinvestigated,normalscreeningofanindividualwouldneedtoextendformorethan60secondsforanindividualtobeexposedtoradiationthatexceedstheANSI/HPSN43.172009limit.Incomparison,atypicalscreentakesabout6seconds. KeyRecommendation:FutureX-rayadvancedimagingtechnology(AIT)systemsshouldhavesomeindependentmechanismtoensurethattheAITsystemdoesnotscreenanypersonforlongerthanthetimeneededtoacquiretheappropriateimagewhilekeepingradiationexposurecompliantwiththesafetyprincipleofaslowas(is)reasonablyachievable. KeyRecommendation:Anyfuturetestingproceduresshouldataminimumcontinuetofollowtheindicators,controls,andsafetyinterlocksrequirementsoftheANSI/HPSN43.17-2009standard,orsimilartestingprocedures,andincludedailyverificationofsafetyparametersbyatestpiece. DoseComputations Thecommittee’sapproachinexaminingthedosetotheindividualbeingscreeneddiffersfromthatofpreviousinvestigationsintwoways: Itmadeuseofsensitivedetectorswithtissue-equivalentphantomstoverifybeamintensity,X-rayquality,andpenetration;and Itperformedcomputationsusingestimatesofbeamintensity,scanninggeometry,anddigitizedhumanphantomsthathaverealisticdimensionsandmorphology. Page153 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Basedontheseimprovedconditions,thecommitteestatesthat: KeyFinding:Underroutineoperations,thecomputedeffectivedosesusingrealisticcomputationalX-raysourcesandscanninggeometries,coupledwiththedigitizedhybridphantoms,aresimilartotheANSIreferenceeffectivedoseandanorderofmagnitudebelowthelimitof250nSv/screen,assetforthintheapplicableANSIstandard. KeyFinding:ForeithertheRapiscanSecure1000ortheAS&ESmartChecksystems,asdeterminedbythecommitteeforadultsandchildren: TheeffectivedosesareaboutthesameasthosecalculatedfollowingthesimplifiedformulaforthereferenceexposuredoseidentifiedbytheANSI/HPSN43.17-2009standard; Theeffectivedosesarelowerthanthoseinpreviousreportsusingplane-parallelX-raybeamswithstylizedgeometrical(low-fidelity)humanphantoms;and Sensitivityanalysisshowedthatunderarangeofdifferentconditions,includingpassengerpositionintheAITsystemandincreasesintheenergy(i.e.,byincreasingthetubehighvoltage)oftheX-raybeam,thecomputedeffectivedosewouldnotincreasebymorethanafactorof3and,evenso,itwouldremainwellbelowthelimitspecifiedintheANSI/HPSN43.17-2009standard. Section6.1.1.1ofANSI/HPSN43.17-2009specifiesthattheexposurelimitationsis“basedonacomputationaladultmodelandisnotalwaysindicativeoftheactualeffectivedoes,especiallyforsmallchildren.”Section6.1.1.1alsoreferstoaradiationdoseforafull-bodyscan.TheNRCsubcontractor’scalculationsenabledthecommitteetoestimatevariationsinabsorbeddosenotcapturedintheANSIstandard.Thisincludeddetailsofabsorbeddosedistributionsinawidevarietyofbodytypes,includingchildrenandthedevelopingfetus,aswellasspecificorgansineachofthosebodytypes.Understandardoperatingconditions,thecommitteefoundthat: KeyFinding: Noperson,regardlessofageandweightmodeled,wouldexceedtheeffectivedoselimitperscreen(i.e.,250nSv/screen),asdefinedbytheANSI/HPSN43.17-2009standard; Theabsorbeddoseperscreentothedevelopingfetusatanyofthethreestagespost-conceptionislessthan0.0003percentoftherecommendedlimitforradiationprotectionofthefetusduringtheentiregestationperiod; Page154 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Theabsorbeddosetotheepitheliallayerofradiosensitivecellsintheskinisnotsignificantlyelevated(~1.6percent)comparedtotheaveragedosetotheskin;and Thedosereceivedbythelensoftheeye,skin,orfemalebreastduringastationarybeamofXraysforthedurationofthescanwereatleast2ordersofmagnitudebelowthresholdswheretissueinjurymightoccur. ItmightbeworthmentioningthatMoweryetal.40indicatethatduringtheworst-casescenario,whenallinterlocksaredefeatedbymaliciouscode,theAITsystemcanbeinstructedtodeliverthewholeradiationdosefromascantoasinglerandompointonthebody.Ifthisworst-casescenariooccursandtherandomdeliveryofthedoseactuallyhappenstobeintheworstplacepossible,theeye,thecomputationspresentedaboveindicatethatthisdoseisatleast2ordersofmagnitudebelowthethresholdwheretissueinjurymightoccur.ThisfactpointsouthowimportantthepreviousrecommendationisthatthereissomeindependentmechanismtoensurethattheAITdoesnotscreenanypersonforlongerthanthetimeneededtoacquiretheappropriateimage. KeyFinding:TheagreementbetweentheestimateddoseresultsfromtheNRCsubcontractorandtheresultsfrompreviousstudiesconfirmsthatthecalculationsperformedinpreviousstudieswereadequatetoestablishcompliancewitheffectivedoselimitsrecommendedinANSI/HPSN43.17-2009. _______________ 40K.Mowery,E.Wustrow,T.Wypych,C.Singleton,C.Comfort,E.Rescorla,S.Checkoway,J.A.Halderman,andH.Shacham,Securityanalysisofafull-bodyscanner,Proceedingsofthe23rdUSENIXSecuritySymposium,2014,https://www.usenix.org/conference/usenixsecurity14/technical-sessions/presentation/mowery. Page86 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page87 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page88 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page89 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page90 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page91 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page92 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page93 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page94 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page95 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page96 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page97 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page98 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page99 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page100 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page101 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page102 Share Cite 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SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page107 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page108 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page109 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page110 Share Cite 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SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page153 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Page154 Share Cite SuggestedCitation:"7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems."NationalAcademiesofSciences,Engineering,andMedicine.2015.AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards.Washington,DC:TheNationalAcademiesPress.doi:10.17226/21710.× Save Cancel Next:Appendixes» AirportPassengerScreeningUsingBackscatterX-RayMachines:CompliancewithStandards GetThisBook × BuyPaperback|$69.00 BuyEbook|$54.99 MyNAPmemberssave10%online. LoginorRegistertosave! DownloadFreePDF PassengerscreeningatcommercialairportsintheUnitedStateshasgonethroughsignificantchangessincetheeventsofSeptember11,2001.Inresponsetoincreasedconcernoverterroristattacksonaircrafts,theTransportationSecurityAdministration(TSA)hasdeployedsecuritysystemsofadvancedimagingtechnology(AIT)toscreenpassengersatairports.Todate(December2014),TSAhasdeployedAITsinU.S.airportsoftwodifferenttechnologiesthatusedifferenttypesofradiationtodetectthreats:millimeterwaveandX-raybackscatterAITsystems.X-raybackscatterAITsweredeployedinU.S.airportsin2008andsubsequentlyremovedfromallairportsbyJune2013duetoprivacyconcerns.TSAislookingtodeployasecond-generationX-raybackscatterAITequippedwithprivacysoftwaretoeliminateproductionofanimageofthepersonbeingscreenedinordertoalleviatetheseconcerns. ThisreportreviewspreviousstudiesaswellascurrentprocessesusedbytheDepartmentofHomelandSecurityandequipmentmanufacturerstoestimateradiationexposuresresultingfrombackscatterX-rayadvancedimagingtechnologysystemuseinscreeningairtravelers.AirportPassengerScreeningUsingBackscatterX-RayMachinesexamineswhetherexposurescomplywithapplicablehealthandsafetystandardsforpublicandoccupationalexposurestoionizingradiationandwhethersystemdesign,operatingprocedures,andmaintenanceproceduresareappropriatetopreventoverexposuresoftravelersandoperatorstoionizingradiation.ThisstudyaimstoaddressconcernsaboutexposuretoradiationfromX-raybackscatterAITsraisedbyCongress,individualswithinthescientificcommunity,andothers. Contents FrontMatter i–xviii Summary 1–8 1Introduction 9–26 2RadiationPhysicsRelevanttoAdvancedImagingTechnology 27–32 3X-RayBackscatterAdvancedImagingTechnology 33–39 4DosimetryforX-RayBackscatterAdvancedImagingTechnology 40–47 5RadiationProtectionStandards 48–55 6ReviewofX-RayBackscatterAdvancedImagingTechnologyStudies 56–85 7Measurements,DoseCalculations,andSystemDesignforX-RayBackscatterAdvancedImagingTechnologySystems 86–154 Appendixes 155–156 AppendixA:StatementofTask 157 AppendixB:Glossary,Acronyms,andAbbreviations 158–162 AppendixC:OrganAbsorbedDoses 163–169 AppendixD:SummaryofStatisticsfromPreviousStudies 170–175 AppendixE:BiographiesofCommitteeMembersandContractors 176–184 × WelcometoOpenBook! You'relookingatOpenBook,NAP.edu'sonlinereadingroomsince1999.Basedonfeedbackfromyou,ourusers,we'vemadesomeimprovementsthatmakeiteasierthanevertoreadthousandsofpublicationsonourwebsite. DoyouwanttotakeaquicktouroftheOpenBook'sfeatures? 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