X射线剂量学（一）

X射线剂量学（一）放射治疗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）射线照射野中心轴剂量学参数SSD1SSD2D2D3D4D5D6D1dmdc空气水模体dm参考深度dc校准深度距离平方反比定律距离平方反比定律（续）D1:D2

空气中两点剂量比值，等于其距源距离平方的反比近源处剂量跌落的速率，快于远源处照射野中心轴百分深度剂量D4:D3PDD=D4/D3X100%

影响PDD的因素射线能量皮肤剂量建成深度最大剂量深度深度照射野大小等效方野原射线和散射线源皮距离平方反比定律6MVX射线百分深度剂量图15MVX射线百分深度剂量图Part2,lecture2:Dosimetryandequipment18PercentagedepthdosemeasurementVariationofdoseinamedium(typicallywater)withdepthIncludesattenuationandinversesquarelawcomponentsPart2,lecture2:Dosimetryandequipment19PercentagedepthdoseRelatesdoseatdifferentdepthsinwater(orthepatient)tothedoseatthedepthofdosemaximum-notethattheyaxisisrelative!!!百分深度剂量影响因素：模体中深度照射野大小源皮距离射线能量Part5,lecture1:Radiationtypesandtechniques21Build-upeffect

Resultoftheforwarddirectionofsecondaryelectrons-theydepositenergydownstreamfromtheoriginalinteractionpoint剂量建成表面剂量:•100%浅层X射线•30%钴-60γ射线•15%6MVX射线•10%18MVX射线

不同能量光子束百分深度剂量曲线

SAD条件组织空气比（TAR）D4:D2TAR=D4/D2D3:D1BSF=D3/D1（参考深度的TAR,反散因子）TAR影响因素：模体中深度照射野大小射线能量组织模体比（TPR）/组织最大剂量比（TMR)D5:D3TMR=D5/D3D6:D4TPR=D6/D4TPR影响因素：模体中深度照射野大小射线能量TMR影响因素：模体中深度照射野大小射线能量Part2,lecture2:Dosimetryandequipment30TMR,TPRMimicsisocentricconditionsTMRisaspecialcaseofTPRwherethereferencephantomdepthisdepthofmaximumdosePart2,lecture2:Dosimetryandequipment31PDDandTMRPercentagedepthdose(PDD)changeswithdistanceofthepatienttothesourceduetovariationsintheinversesquarelaw(ISL),TAR,