X射線劑量學（一）放射治療Part2,lecture1:Generalradiationphysics3XRayproductionHighenergyelectronshita(metallic)targetwherepartoftheirenergyisconvertedintoradiationtargetelectronsXRaysLowtomediumenergy(10-400keV)High>1MeVenergyPart2,lecture1:Generalradiationphysics4XRayTubeforlowandmediumXRayproductionPart2,lecture1:Generalradiationphysics5MegavoltageXRaylinacPart1:Introductorylecture6Superficial/orthovoltageunitPart1:Introductorylecture7ModernCobalt60unitPart1:Introductorylecture8LinearacceleratorwithelectronconeElectronapplicatorPart10,lecture2:Dosimetry9ToolsforcommissioningMainlyscanningwaterphantomDetermineallpropertiesofallradiationbeamsdepthdose,TPRprofileswedgesblocks,...Part2,lecture2:Dosimetryandequipment10ScanningwaterphantomPart10,lecture2:Dosimetry11TreatmentunitcommissioningAspects:SafetyVerificationthatspecsaremetOtherbitsandpiecesrequiredforplanningManyprotocolsandguidelinesavailableUsuallydoneusingawaterphantomandslabphantomsSignificanttimecommitment-however,accessisusuallynotaproblemX（γ）射線照射野中心軸劑量學參數SSD1SSD2D2D3D4D5D6D1dmdc空氣水模體dm參考深度dc校準深度距離平方反比定律距離平方反比定律（續(xù)）D1:D2

空氣中兩點劑量比值，等于其距源距離平方的反比近源處劑量跌落的速率，快于遠源處照射野中心軸百分深度劑量D4:D3PDD=D4/D3X100%

影響PDD的因素射線能量皮膚劑量建成深度最大劑量深度深度照射野大小等效方野原射線和散射線源皮距離平方反比定律6MVX射線百分深度劑量圖15MVX射線百分深度劑量圖Part2,lecture2:Dosimetryandequipment18PercentagedepthdosemeasurementVariationofdoseinamedium(typicallywater)withdepthIncludesattenuationandinversesquarelawcomponentsPart2,lecture2:Dosimetryandequipment19PercentagedepthdoseRelatesdoseatdifferentdepthsinwater(orthepatient)tothedoseatthedepthofdosemaximum-notethattheyaxisisrelative!!!百分深度劑量影響因素：模體中深度照射野大小源皮距離射線能量Part5,lecture1:Radiationtypesandtechniques21Build-upeffect

Resultoftheforwarddirectionofsecondaryelectrons-theydepositenergydownstreamfromtheoriginalinteractionpoint劑量建成表面劑量:?100%淺層X射線?30%鈷-60γ射線?15%6MVX射線?10%18MVX射線

不同能量光子束百分深度劑量曲線

SAD條件組織空氣比（TAR）D4:D2TAR=D4/D2D3:D1BSF=D3/D1（參考深度的TAR,反散因子）TAR影響因素：模體中深度照射野大小射線能量組織模體比（TPR）/組織最大劑量比（TMR)D5:D3TMR=D5/D3D6:D4TPR=D6/D4TPR影響因素：模體中深度照射野大小射線能量TMR影響因素：模體中深度照射野大小射線能量Part2,lecture2:Dosimetryandequipment30TMR,TPRMimicsisocentricconditionsTMRisaspecialcaseofTPRwherethereferencephantomdepthisdepthofmaximumdosePart2,lecture2:Dosimetryandequipment31PDDandTMRPercentagedepthdose(PDD)changeswithdistanceofthepatienttothesourceduetovariationsintheinversesquarelaw(ISL),TAR,