Evaluation of the Influence of Lung Inhomogeneity on Depth Dose Distribution before and after the Lung in Electron Therapy: A Semi-Experimental Study

[摘要] BackgroundandObjective:Becauseofthevastusageofhighenergyelectronbeamsinirradiationofthechestwallandthepossibilityofexposingthewholeorapartoflungintheirpathsandsignificantuncertaintyincalculatingtheabsorbeddosecausedbythisinhomogeneity,evaluationoftheinfluenceoflunginhomogeneityondepthdosedistributionbeforeandafterthelungisnecessary.SubjectsandMethods:Threecorkplatesaslung-equivalenttissueswithdifferentthicknessesof1,2and3centimeterwereplacedinawaterphantomandabsolutedosimetrywasdonebyPPC40ionchamberforbeamenergiesof9,12and15MeVgeneratedbySiemensPrimusPluslinearacceleratorindifferentfieldsizesof2r=5,10×10and15×15cm².Inaddition,somecorrectionfactorswerecalculatedbyeffectiveSSDmethodfordifferentbeamenergiesandwereexertedonprimarydatainthissemi-experimentalstudy.ForsubsequentcomparisonstoevaluatetheCETmethod,dosimetryalsowasdoneatdepthsof1.5,1.8,2.2,2.5and3.5centimeterinhomogeneouswaterphantom.Results:Afterexertingcorrectionfactorsonprimarydata,forallthicknessesofinhomogeneoustissue,energiesandfields,theabsorbeddosebeforetheinhomogeneityislowerandtheabsorbeddoseaftertheinhomogeneityishigherthantheabsorbeddoseatitsequivalentdepthsinhomogeneouswaterphantom.Fortheenergyof9MeVinthefieldof2r=5,theerrorpercentageofdoseestimationwithCETmethodissignificantlyhigherthanotherenergiesandfields.Thispercentagealsoincreasesbyincreasingininhomogeneitythicknessforallenergiesinthe2r=5field.Conclusion:Incomparisonwithdepthdoseinhomogeneousphantom,thelung-equivalenttissueresultsdosereductionbeforeanddoseincreaseafterthelung.Inaddition,theerrorpercentageofCETmethodinsmallerfieldandenergyissignificantlyhighanditsapplicationinsimilarcasesisnotrecommended.

[学科分类] 基础医学