辐射防护及医用体内辐射剂量.ppt

RadiationProtectionandMedicalInternalDosimetry輻射防護及醫用體內輻射劑量,高雄醫學大學附設中和紀念醫院核子醫學科陳毓雯主任,PatternofRadiationEffect,ExposureContamination,UnitsofRadiationDose,Activity(A)BqRadiationexposureC/kgAirkeramaAbsorbeddose(D)grayEquivalentdose(H)sievertLET(linearenergytransfer)Effectivedose(E),ConversionsofUnits,ThresholdDosesforDetermininsticEffectsinTheMoreRadiosensitiveTissuesandOrgans,BiologicalEffectsofExposure,NonstochasticeffectsStochasticeffects,ProbabilityofRiskofFatalCancerbetweenAgeandSex,DoseinMedicalImaging,AnnualEffectiveDoseDistributioninTheWorld,InternalDosimetry,ThemethodofcalculatingabsorbeddosedeliveredinternallyhasbeendevelopedovermanyyearsbytheMedicalInternalRadiationDose(MIRD)committeeoftheAmericanSocietyofNuclearMedicine.Theaimofcommitteewastodevelopadosimetrysystem(MIRDschema)fordiagnosticnuclearmedicine.However,themethodshavealsobeenappliedinradionuclidetherapyandininternalcontamination.,MIRDSchema,SourceOrgansvsTargetOrgansDts=AsStsCumulatedactivity,Asthetotalnumberofradioactivedisintegrationswhichoccurinthesourveorgan,anddependson:theactivityadministered;theuptakeof,retentionby,andexcretionfromtheorgan;andthtephysicaldecayoftheradionuclide.S-factorshavebeentabulatedforavarietyofradionuclidesandfordifferentsource/targetconfigurationsinbothstandardmanandchildren.,CumulatedActivity,FlowChartofMIRDMethology,S-Factors,Sts=1/miiiiequilibriumabsorbeddoseconstantiabsorbedfractionspecificabsorbedfraction(MonteCarlocalculations),Example,Calculatedtheabsorbeddosetotheliverofanadultpatientwhoreceives3mCi(111MBq)Tc99m-sulfurcolloidforaliverscan,assuming85%liveruptakewithnoexcretion.AnswerWeightofliver=1700g(forastandardman)A0intheliver=3000 x0.85=2550uCi(86.7MBq)Te=6hrii=0.0806D=1.44x(2550/1700)x6x0.0806=1.04rad,ThelimitationsoftheMIRDMethods,TabulateddosesdonotapplytoallpatientsIntheMIRDschemaitisassumedthattheshape,sizeandpositionoftheorgansaresprepresentedbythestandard,70kg,hermaphroditehumanphantom.Diseaseorganscanresultinbothincreasedordecreaseduptakeofactiviityandchangesintheresidencetimecomparedwithstandardvaluessothesefactorssholudalsobeconsideredwhenassessingthedosetopatients.TheMIR