photon/electron specific absorbed fractions for icrp ... fall... · photon/electron specific...
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PHOTON/ELECTRONSPECIFICABSORBEDFRACTIONSFORICRPPEDIATRICPHANTOMSBCSchwarz,Ph.D.WJGodwin,M.S.WEBolch,Ph.D.
2016FLAAPMFallMeeting9/9/2016
NRCRegulations• NRCRegulations
• HodgepodgeofdifferentrecommendationsfromICRP• RangingfromICRP1(1959)toICRP60(1991)
• PrimarilybasedonICRP26(1977)
• 10CFRPart20– May1991Revision• IncorporatedbasicmethodsanddatafromICRP26(1977)• ICRP30usedforinternaldosecalculations
• Since1991revision,numerousICRPpublicationsreleased
• ManyofthepublicationshaveupdatedthemodelsfromICRP26andICRP30
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StylizedPhantoms
• Mathematicalphantoms
• Organ/bodycontoursbasedonshapesandequations
• Hermaphroditic
• Easytoutilize• Organsize/shapeflexibility• Lessmemoryintensive
ICRP60,ICRP103• Providedupdatedrecommendationstothecalculationofdose• Modifiedmodelsforcalculatingradiationexposure• Adjustedweightingfactors• Modifiedmetabolicmodelsofradioactivematerialinhumans
• Notableadjustmentscomparedto10CFR20• Changesinterminology(ICRP60)• Changesintissueweightingfactors(ICRP60,ICRP103)• Changesinradiationweightingfactors(ICRP103)
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TissueWeightingFactors– 1977toPresent
VoxelPhantoms(1)
• DerivedthroughsegmentationofCT/MRimagesets
• Highlyaccuratetohumananatomy
• Highlyspecifictoparticularpatient
• Adjustmentsnotassimple
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VoxelPhantoms(2)
• ICRPreferencecomputationalphantomsdeveloped• ICRP89forreferenceanatomicalinformation
• Specifictomalesandfemales
• Multipleagegroups• Adult(ICRP110)• Adolescents,Children?
ICRPReferencePediatricVoxelPhantoms
• BaseduponUF/NCIhybridphantomseries
• TraceabletoCTimagesofage/sizematchedpatients
• Additionalorgan/tissuemodelsforICRPreferencephantoms
• Correctionstotissuemodels
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Updating10CFRPart20?• UpdatedmodelavailabilityforagegroupsprovidesabundanceofinformationfornextupdateofNRCregulations
• Current10CFRPart20• Generalmethodologybasedonadults
• Moreprudenttoincludemultipleageswithinregulations?• Age‐ andgender‐averagedmethodology• Morerealisticrepresentationofthegeneralpopulation
• ForapplicationofupdatedICRPpublicationsbyU.S.federalagencies,effectivedosecoefficientsnecessary• Introductionofeffectivedose?
SpecificAbsorbedFraction(SAF)• Fractionofenergyemittedinsourceregionabsorbedpermassoftargetregion
• SAFisprimaryphysicaldatausedindosimetryofinternalemitter• Usedwithbiokineticdataofradionuclidetodetermineorgandoses• SAF,radiationinformation,radiationweightingfactor SValue• SValue,integratedactivity doseratetoorgan
← ,
,
, ← ,
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DerivingSAFs• Derivedforseriesofmonoenergeticradiations(Ei)
• Valuesforspecificradiationemittedbyradionuclidederivedbyinterpolationofenergyemission
• SAFdataderivedusingcomputationalMonteCarlomethodswithcomputationalphantoms
• Endgoal• SAFforeachsource‐targetcombinationasdefinedwithinICRPframework
• SAFforeachageandgender• SAFsforallradiationsnecessaryforNRCregulationsupdate
ApplicationofSAFs
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PreviousStudies• Previousstudy:Wayson(2012)
• DevelopedextensiveSAFdatasetsforpediatricUFhybridphantomseries
• Recentandfinalchangestophantomseries• ICRPreferencepediatricvoxelphantoms
• Repairofwalledorgans(e.g.SI‐wall)• Correctionstolymphnodemodel• Correctionstomusclemodel• Revisedmodelsofbreast,oralmucosa,andureters
• Source/targetorgans• Decisiontoextendto10MeVparticles
ChangestoPhantomMuscleModel
Generation1 Generation2 Current
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Goals• ReplaceUF‐Waysonpediatricphoton/electronSAFdatasetswithnewfinaldatasets
• Providefinalphoton/electronSAFdatasetsforadoptionbyICRPasreferencestandard
• ProvideSAFdatasetstofederalagenciesforcalculationofradionuclideSvaluesforusebyfederalagenciesinfutureregulations
PhotonSAFs– LowEnergies• Lowenergyinterpolation
• 0keVSAFcalculatedusingcurrentICRPmethodology• Log‐loginterpolationto0keVvalue• Source‐targetcombinationdetermineslimitingSAF
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PhotonSAFs
Φ(liver liver) Φ(muscle lungs)
PhotonSAFs– GenderDifferencesΦ(thyroid thoraciclymphnode)
ICRP00F ICRP00M
Φ(thyroid urinarybladdercontents)
ICRP00MICRP00F
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ElectronSAFs– Approach
CEL SAF
Φ ← ,
∗
Electron collisional component
• Monoenergetic electrons• Energy deposition from electrons
only• No photon transport
Electron radiative component
• Monoenergetic electrons• Record initial bremsstrahlung
energies• Generate spectrum
REL SAF
Φ ← , ∑ Φ ← ,
∗
Photon SAF
Φ ,
Final Electron SAF
Φ , Φ Φ
BremsstrahlungSpectrum(1)• Initialspectrum– 20,000electronhistories• Source– AnteriorET
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BremsstrahlungSpectrum(2)• Source– AnteriorET• Electronenergy– 400keV• Referencehistories– 20million
BremsstrahlungSpectrum(3)• Resultingspectrum– AnteriorET
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ElectronSAFs(1)
Φ(thyroid thyroid) Φ(muscle liver)
ElectronSAFs(2)
Φ(thyroid urinarybladderwall)Φ(adrenals liver)
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PhantomDiscrepancies
Φ(gallbladderwall liver)
ICRP01MF
ICRP00MF
Summary• NewsetofSAFscompletedforICRPreferencepediatricvoxelphantoms• Photon,electron
• Majorityofdataagreedverywellwithpreviouslygenerateddatasets• PreviousWaysondata• SAFsforICRP110phantoms(upcomingICRPdocument)
• LargevariabilityofelectronSAFdependentonphantomanatomy• Explainedbyinconsistentpositioning• LikelytobecorrectedinfuturebyICRP
• Overall,SAFspresentedrepresentthebackboneofsoon‐to‐beICRPreferenceSAFsforpediatricages
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Acknowledgements• ResearchGroup
• WesleyBolch• WilliamGodwin
• Funding• USDOE• NIH• USEPA
• Others• DerekJokisch(FrancesMarion,ORNL)• ShaheenDewji(ORNL)• MichaelBellamy(ORNL)• ChoonsikLee(NCI)