利用蒙特卡洛模拟评估TrueBeam加速器6 MV非均整模式下相空间文件的通用性  

Assessment of the Versatility of Phase Space Files in TrueBeam Accelerator 6 MV Flattening Filter Free Mode by Monte Carlo Simulation

作　　者：陈蕾 唐华南[1] 傅玉川 李长虎 韩纪锋 CHEN Lei;TANG Huanan;FU Yuchuan;LI Changhu;HAN Jifeng(Center for Radiophysical Technology,Cancer Center,West China Hospital Sichuan University,Chengdu Sichuan 610041,China;Key Laboratory of Radiation Physics and Technology,Ministry of Education,Institute of Nuclear Science and Technology,Sichuan University,Chengdu Sichuan 610064,China)

机构地区：[1]四川大学华西医院肿瘤中心,放射物理技术中心,四川成都610041 [2]四川大学原子核科学技术研究所,辐射物理及技术教育部重点实验室,四川成都610064

出　　处：《中国医疗设备》2023年第9期64-68,共5页China Medical Devices

基　　金：四川省科技计划重点研发项目(2020YFS0274)。

摘　　要：目的探究Varian 6 MV光子束非均整模式(Flattening Filter Free,FFF)下相空间文件(Phase Space File,PSF)对同类加速器的通用性。方法基于我院的Varian Edge加速器头中的组件参数,利用EGSnrc/BEAMnrc分别模拟了完整的加速器头模型(完整FFF模型)和使用Varian提供的6 MV FFF模式PSF输入源的部分加速器头模型(部分FFF模型),使用EGSnrc/DOSXYZnrc模拟两种模型条件下水模体中的剂量分布,得到百分深度剂量(PercentageDoseDepth,PDD)和横向剂量离轴比(Off Axis Ratio,OAR),并与测量数据进行比较,同时对在射野大小10 cm×10 cm下二者在离开加速器头后获得的PSF进行能谱和能量注量的分析。结果Varian提供的6 MV FFF的PSF存在对入射能量和离轴平均能量的低估倾向,从而使其PDD相对测量数据偏低,在OAR跌落区存在较大的偏差。完整FFF模型和部分FFF模型之间存在差异。通过比较两个模型的PDD和OAR数据,发现部分FFF模型的结果略差于完整FFF模型。此外,能谱分析也表明,部分FFF模型的较低入射电子能量会对低能光子占比和离轴平均能量产生影响。结论本研究使用蒙特卡洛软件对利用Varian提供的TrueBeam的6 MV FFF的PSF构建部分FFF模型和完整FFF模型进行模拟,得到的不同射野下水模体的三维剂量分布,结果表明,采用PSF构建的模型存在PDD偏低、OAR偏差大、离轴平均能量低估等问题,建议采用该PSF时,应与实际的水箱测量数据进行对比验证,同时采取具体的措施降低不确定度,若差异较大时,应构建完整的加速器机头模拟参数以适应不同的研究内容。Objective To explore the universality of phase space file(PSF)for similar accelerators under Varian 6 MV photon beam flattening filter free(FFF)mode.Methods Based on the parameters of the Varian Edge accelerator in our hospital,EGSnrc/BEAMnrc was used to simulate a complete accelerator head model(complete FFF model)and a partial accelerator head model(partial FFF model)with PSF input source in 6 MV FFF mode provided by Varian.EGSnrc/DOSXYZnrc was used to simulate the dose distribution in the subsurface model under the two model conditions,and the percentage dose depth(PDD)and the lateral dose off axis ratio(OAR)were obtained,and compared with the measured data.At the same time,the energy spectrum and energy injection of the PSF obtained after leaving the accelerator head at the field size of 10 cm×10 cm were analyzed.Results The PSF of the 6 MV FFF provided by Varian tended to underestimate the incident energy and off axis average energy,resulting in a relatively low PDD compared to the measured data and a significant deviation in the OAR drop zone.There were differences between the complete FFF model and the partial FFF model.By comparing the PDD and OAR data of the two models,it is found that the results of partial FFF models were slightly worse than those of the complete FFF model.In addition,the energy spectrum analysis also showed that the lower incident electron energy of partial FFF models could affect the proportion of low-energy photons and the average offaxis energy.Conclusion In this study,Monte Carlo software was used to construct partial FFF model and complete FFF model by utilizing TrueBeam's 6 MV FFF PSF provided by Varian to simulate the three-dimensional dose distribution of different launching fields.The results shows that the model constructed with PSF has some problems,such as low PDD,large OAR deviation,and underestimation of off-axis average energy.It is suggested that this PSF should be compared and verified with the measurement data of in-house water tanks,and specific measures should be

关 键 词：TrueBeam加速器 蒙特卡洛 非均整模式 Varian Edge加速器 能谱 相空间文件 

分 类 号：R144[医药卫生—公共卫生与预防医学] R197.39