组织替代材料之间的转换

Chapter1fundamentalphysicsofradiationdosimetryThemaincontentsProductionofRadiation（review）Interactionsofionizingradiation（r)Basicconceptsinradiationdosimetry（r）PhantomDosemeasurementmethology1.ProductionofRadiationTheclassificationofradiation1.ProductionofRadiationTheclassificationofradiation1.ProductionofRadiationTheclassificationofradiationBothdirectlyandindirectlyionizingradiationsareusedintreatmentofdisease,mainlybutnotexclusivelymalignantdisease.Thebranchofmedicinethatusesradiationintreatmentofdiseaseiscalledradiotherapy,therapeuticradiologyorradiationoncology.Diagnosticradiologyandnuclearmedicinearebranchesofmedicinethatuseionizingradiationindiagnosisofdisease.1.ProductionofRadiationThekindofrayscanbeusedforradiationtherapy：X-raysγ-raysElectronbeamNeutronbeamandprotonbeam1.ProductionofRadiationX-rayswerediscoveredbyRoentgenin1895whilestudyingcathoderaysinagasdischargetube.Heobservedthatanothertypeofradiationwasproduced(presumablybytheinteractionofelectronswiththeglasswallsofthetube)whichcouldbedetectedoutsidethetube.Thisradiationcouldpenetrateopaquesubstances,producefluorescence,blackenaphotographicplate,andionizeagas.Henamedthenewradiationx-rays.1.ProductionofRadiation1.1ProductionofX-RaysTherearetwodifferentmechanismsbywhichx-raysareproduced.Onegiverisetobremsstrahlungx-rays(brakingradiation)andtheothercharacteristicx-rays.1.ProductionofRadiation1.1.1Kilovoltageunits(eliminatedthroughselectionorcontest)(千伏级x线机)Grenz-raytherapy:usedtodescribetreatmentwithbeamsofverysoft(low-energy)x-raysproducedatpotentialsbelow20kVContacttherapy:potentialsof40to50kVSuperficialtherapy:from50to150kVOrthovoltagetherapyordeeptherapy:from150to500kVSupervoltagetherapy(high-voltage):500to1000kVMegavoltagetherapy:1MVorgreater1.ProductionofRadiation1.1.2Medicallinearaccelerator(直线加速器)4MV,6MV,8MV,10MV,15MV,25MV表1钨靶x线管和加速器产生x线的效率加速电压40KV70KV100KV150KV4MeV20MeVX线能（%）0.40.60.81.33670热能（%）99.699.499.298.764301.ProductionofRadiation1.2γ-raysSourceRa-226(镭-226)Cs-137(铯-137)halfoflife:33yCo-60(钴-60)5.27y1.25MeVI-125(碘-125)usedforbrachytherapyIr-192(铱-192)usedforbrachytherapyNucleustransformationQYXQYXQHYXAZAZAZAZAZAZ114242e2.Interactionsofionizingradiation2.1InteractionsofelectronradiationElectroninteractswithmatterthroughCoulombinter-actionswithatomicorbitalelectronsandatomicnuclei.Throughthesecollisionstheelectronsmaylosetheirkineticenergy(collisionandradiativelosses)orchangetheirdirectionoftravel(scattering).Energylossesaredescribedbystoppingpower;scatteringisdescribedbyscatteringpower.2.InteractionsofionizingradiationInteractionofanelectronwithanatom,whereaistheatomicradiusandbtheimpactparameter.2.InteractionsofionizingradiationInteractionsofelectronradiationorbitalelectroninteractionsCoulombinteractionsbetweentheincidentelectronandorbitalelectronsofanabsorberresultinionisationsandexcitationsofabsorberatoms:Ionisation:ejectionofanorbitalelectronfromabsorberatom;Excitation:transferofanorbitalelectronoftheabsorberatomfromanallowedorbittoahigherallowedorbit(shell);Atomicexcitationsandionisationsresultincollisionalenergylossesandarecharacterizedbycollision(ionisation)stoppingpowers.2.InteractionsofionizingradiationInteractionsofelectronradiationElectron-nucleusinteractionsCoulombinteractionsbetweentheincidentelectronandnucleioftheabsorberatomresultinelectronscatteringandenergylossoftheelectronthroughproductionofx-rayphotons(bremsstrahlung).Thesetypesofenergylossesarecharacterizedbyradiativestopping2.Interactionsofionizingradiation2.2InteractionsofxorγraybeamWhenanxorγraybeampassesthroughamedium,interactionbetweenphotonsandmattercantakeplacewiththeresultthatenergyistransferredtothemedium.Theinitialstepintheenergytransferinvolvestheejectionofelectronsfromtheatomsofabsorbingmedium.Thesehigh-speedelectronstransfertheirenergybyproducingionizationandexcitationoftheatomsalongtheirpaths.2.InteractionsofionizingradiationIftheabsorbingmediumconsistsofbodytissues,sufficientenergymaybedepositedwithinthecells,destroyingtheirreproductivecapacity.However,mostoftheabsorbedenergyisconvertedintoheat,producingnobiologiceffect.2.InteractionsofionizingradiationThefollowingaretheactionformsintheinteractionbetweenphotonandmedium.Photoelectriceffect光电效应Comptoneffect康普顿效应Pairproduction电子对产生Coherentscattering相干散射Interactionofphotonandnucleus光核反应2.Interactionsofionizingradiation光电效应康普顿效应电子对效应光子与介质相互作用产生高速电子主要通过三个过程2.Interactionsofionizingradiation2.2.1PhotoelectricEffectThephotoelectriceffectisaphenomenoninwhichaphotoninteractswithanatomandejectsoneoftheorbitalelectronsfromtheatom.Inthisprocess,theentireenergyhvofthephotonistransferredtotheatomicelectron.Thekineticenergyoftheejectedelectron(calledthephotoelectron)isequaltohv-EB,whereEBisthebindingenergyoftheelectron.InteractionofthistypecantakeplacewithelectronsinK,L,M,orNshells.Photoelectriceffect2.Interactionsofionizingradiation光电效应发生的能量条件是：入射光子的能量必须等于或大于轨道电子的结合能。光电效应的发生几率与物质的原子序数的4次方成正比，与入射线波长的3次方成正比即与光子能量的3次方成反比。33EZ2.Intera