控制点统计不确定度对直肠癌容积旋转调强放疗剂量计算的影响  

Impact of statistical uncertainty per control point on dose calculation on VMAT for rectum cancer

作　　者：叶为镪 张伟[1] 李博[1] 于超俊 韦珍珍[1] 苏世达[1] 覃文[1] 张大伟[1] YE Weiqiang;ZHANG Wei;LI Bo;YU Chaojun;WEI Zhenzhen;SU Shida;QIN Wen;ZHANG Dawei(Department of Radiation Oncology,the First Affiliated Hospital of Guangxi Medical University,Nanning 530021,Guangxi,China)

机构地区：[1]广西医科大学第一附属医院放疗科,广西南宁530021

出　　处：《实用医学杂志》2024年第19期2685-2689,共5页The Journal of Practical Medicine

基　　金：广西壮族自治区卫生健康委员会自筹经费科研课题(编号:Z20200178,Z20191057)。

摘　　要：目的 探讨使用Monaco计划系统X射线体素蒙特卡罗(XVMC)算法在直肠癌容积旋转调强放疗(VMAT)剂量计算中,不同控制点统计不确定度(SUpCP)对于计算精度和计算效率的影响,给出满足临床剂量计算的控制点统计不确定度。方法 选取直肠癌放疗患者19例,在Monaco计划系统中首先设置SUpCP值为3进行VMAT计划优化和剂量计算获取初始计划,再分别设置SUpCP为1~10(间隔为1)重新计算剂量,获得10组共190个VMAT计划剂量分布,评估靶区D_(max)、D_(mean)、D_(95%)、V_(50)、均匀性(HI)和适形度(CI)的差异,同时评估膀胱、小肠和股骨头的剂量,以及统计各组剂量计算所使用时间(T),分别采用Farmer型电离室和矩阵电离室对每个患者计划进行等中心点绝对剂量测量和三维剂量分布验证,分析绝对剂量偏差ΔD_(ISO)和伽马通过率γ_(33)、γ_(32)、γ_(22)。结果 随着SUpCP值增大,靶区D_(max)和HI增大,D_(95%)和V_(50)降低,膀胱的D_(max)增大,T显著降低,γ_(32)、γ_(22)降低(P<0.05)。靶区的D_(mean)和CI、膀胱的D_(mean)、小肠和股骨头的D_(max)和D_(mean)、ΔD_(ISO)和γ_(33)差异无统计学意义(P>0.05)。所有剂量计算结果的绝对剂量偏差ΔD_(ISO)均<1%,三维剂量分布通过率均>90%;SUpCP值<6时,靶区D_(max)不超过处方剂量的110%;SUpCP值>2时,剂量计算时间<5 min。结论 在Monaco计划系统使用XVMC算法进行直肠癌VMAT剂量计算时,建议设置控制点统计不确定度为3~5,可以快速获得较准确的剂量,同时在三维剂量验证伽马通过率分析时建议使用3%2 mm或2%2 mm标准,本研究为直肠癌VMAT的剂量精确计算提供临床应用依据。Objective To investigate the impact of statistical uncertainty per control point(SUpCP)on dose calculation on volumetric modulated arc therapy(VMAT)for rectum cancer,and to analyze the accuracy and efficiency of calculation.Methods 19 patients with rectum cancer undergoing radiotherapy were selected.The initial VMAT plans were generated on Monaco TPS using SUpCP=3,then changed SUpCP in the dose calculation process as follow:10 SUpCPs(1~10)for each patient,and totally190 VMAT dose distributions were obtained.For plan evaluation,D_(max),D_(mean),D95%,V_(50),homogeneity index(HI),conformity index(CI)of the planning target volume(PTV),dissymmetric variations of bladder,small intestine and femoral head,and time calculation(Time)were analyzed.Patient specific quality assurance(PSQA),dose deviation of isocenter(ΔD_(ISO))and passing rate of three-dimensional dose distribution(γ_(33),γ_(32),γ22)between calculated and delivered radiation doses were measured.Results AsSUpC increased,D_(max) and HI of PTV,D_(max) of bladder were increased,but D95%and V_(50) of PTV,Time,γ_(32) andγ22 were decreased(P<0.05).D_(max) and CI of PTV,D_(mean) of bladder,D_(max) and D_(mean) of small intestine and femoral head,ΔD_(ISO) andγ_(33) showed no statistical significance(P>0.05).WhenΔD_(ISO)<1%,gamma passing rate>90%for all VMAT plan.When SUpCP<6,D_(max) of PTV<110%of the prescribed dose was obtained;while SUpCP>2,time for dose calculation was less than 5 min.Conclusion For VMAT plan of rectum cancer on Monaco TPS using XVMC algorithm,3%~5%of statistical uncertainty per control point for dose calculation,and 3%2 mm or 2%2 mm gamma criteria for three-dimensional dose verification is recommended.This study provides clinical application basis for precise dose calculation of VMAT plan of rectum cancer.

关 键 词：控制点统计不确定度 直肠癌 容积旋转调强放疗 剂量计算 

分 类 号：R735.3[医药卫生—肿瘤] R811.1[医药卫生—临床医学]