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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)