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1、輻射防護及醫(yī)用體內(nèi)輻射劑量UnitsofRadiationDoseActivity(A)BqRadiationexposureC/kgAirkeramaAbsorbeddose(D)grayEquivalentdose(H)sievertLET(linearenergytransfer)Effectivedose(E)ConversionsofUnitsThresholdDosesforDetermininsticEffectsinTheMoreRadiosensitiveTissuesandOrgansBiological
2、EffectsofExposureNonstochasticeffectsStochasticeffectsProbabilityofRiskofFatalCancerbetweenAgeandSexDoseinMedicalImagingAnnualEffectiveDoseDistributioninTheWorldInternalDosimetryThemethodofcalculatingabsorbeddosedeliveredinternallyhasbeendevelopedovermanyyearsbythe
3、MedicalInternalRadiationDose(MIRD)committeeoftheAmericanSocietyofNuclearMedicine.Theaimofcommitteewastodevelopadosimetrysystem(MIRDschema)fordiagnosticnuclearmedicine.However,themethodshavealsobeenappliedinradionuclidetherapyandininternalcontamination.MIRDSchemaSou
4、rceOrgansvsTargetOrgansDts=AsStsCumulatedactivity,Asthetotalnumberofradioactivedisintegrationswhichoccurinthesourveorgan,anddependson:theactivityadministered;theuptakeof,retentionby,andexcretionfromtheorgan;andthtephysicaldecayoftheradionuclide.S-factorshavebeentab
5、ulatedforavarietyofradionuclidesandfordifferentsource/targetconfigurationsinbothstandardmanandchildren.CumulatedActivityFlowChartofMIRDMethologyS-FactorsSts=1/mi?Δi?iΔiequilibriumabsorbeddoseconstant?iabsorbedfractionspecificabsorbedfraction(MonteCarlocalculations)
6、ExampleCalculatedtheabsorbeddosetotheliverofanadultpatientwhoreceives3mCi(111MBq)Tc99m-sulfurcolloidforaliverscan,assuming85%liveruptakewithnoexcretion.AnswerWeightofliver=1700g(forastandardman)A0intheliver=3000x0.85=2550uCi(86.7MBq)Te=6hrΔi?i=0.0806D=1.44x(2550/17
7、00)x6x0.0806=1.04radThelimitationsoftheMIRDMethodsTabulateddosesdonotapplytoallpatientsIntheMIRDschemaitisassumedthattheshape,sizeandpositionoftheorgansaresprepresentedbythestandard,70kg,hermaphroditehumanphantom.Diseaseorganscanresultinbothincreasedordecreasedupta
8、keofactiviityandchangesintheresidencetimecomparedwithstandardvaluessothesefactorssholudalsobeconsideredwhenassessingthedosetopatients.TheMIRDsche
