补偿膜下空腔对放疗计划系统计算浅层剂量的影响  

Effect of Cavity under Bolus on Shallow Dose Calculated by Radiotherapy Planning System

作　　者：孔栋[1] 孔旭东[1] 惠琳 魏贤顶[1] 赵于天 杨波[1] Kong Dong;Kong Xudong;Hui Lin;Wei Xianding;Zhao Yutian;Yang Bo(Department of Radiation Oncology,Affiliated Hospital of Jiangnan University,Wuxi 214062,Jiangsu,China)

机构地区：[1]江南大学附属医院肿瘤放疗科,江苏无锡214062

出　　处：《肿瘤预防与治疗》2021年第1期64-69,共6页Journal of Cancer Control And Treatment

基　　金：无锡市医学发展学科(编号:A2017613);无锡市卫生健康委科研青年项目(编号:Q201917);无锡市卫生健康委转化医学项目(编号:ZM012)。

摘　　要：目的∶基于蒙卡方法研究补偿膜下空腔对放疗计划系统计算浅层组织剂量的影响,为放疗定位及计划制定和评估提供参考与依据。方法∶在Elipe和XIO中分别构建上覆不含或含有不同大小空腔的1cm厚水膜的30 cm×30 cm×30 cm水模体,上表面位于源轴距并垂直于射野中心轴,分别采用各向异性分析算法和超级迭加算法计算不同补偿膜时水模体中心轴和浅层x轴上剂量分布;用Geant4构建加速器模型和相同水模体及水膜,并计算相同位置剂量分布;以Gean4结果为基准评估空腔对Elipse和XO的影响。结果;补偿膜下有空腔时Eclipe和XIO会高估空腔下浅层剂量;空腔厚度不大于0.5cm时,影响约2%,厚度增加影响迅速增加;空腔面积较小,Eclipse和XIO会高估对应区域剂量,随面积增加,对应区域所受影响减小,影响较大区域外移;空腔的影响主要在0.5cm深度内,随深度增加影响迅速减小。结论∶补偿膜下空腔会使Elipe和XO高估浅层剂量,定位时应将空腔厚度控制在0.5 cm以内,面积越小越好;空腔较大建议重新定位。Objective:To study the effect of cavity under bolus on the shallow dose base on Monte Carlo methods.Methods:A 30 cm×30 cm×30 cm water phantom was constructed with a water film(with or without different cavities)of 1 cm thick adjacent to the upper surface of it in the Eclipse and XIO Treatment Planning Systems,respectively.The upper surface of the water phantom was located at source-axis distance and was perpendicular to the central axis of the field.Doses of central axis and x-axis of different models were calculated with analytical anisotropic algorithm and superposition algorithm,respectively.The accelerator model and the same water phantom with bolus models were constructed in Geant4,doses of same positions were also calculated with it.Based on the Geant4 results,the effects of different cavities on dose calculation with E-clipse and XIO were evaluated.Results:Eclipse and XIO would overestimate the shallow dose for cavity under bolus.If the thickness of cavity was not greater than 0.5 cm,the calculation by Eclipse and XIO was affected by about 2%;as the thickness increased,the effect on them raised rapidly.If the area of a cavity was small,Eclipse and XIO would overestimate the dose of the area;as the area increased,the effect on central region decreased;the region which was badly affected gradually moved out until the edge of the field.The effect of cavities on Eclipse and XIO mainly occurred in the region not deeper than 0.5 cm;as the depth increased,the ef decreased rapidly.Conclusion:Carity under bolus would alow Eelipse and XI0 to overestimate the shallow dose.When positoning,the thickness of the eavity should be controlled within 0.5cm,and the smallere the area is,the better.It is reommnended to renew the localialion if the cavity is large.

关 键 词：补偿膜 空腔 GEANT4 治疗计划系统 浅层剂量 

分 类 号：R730.55[医药卫生—肿瘤]