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Study of Calculation Method for 3D Dose Distribution and Range Distribution in a Patient Body in Proton Therapy

质子治疗中患者体内3D剂量分布和范围分布计算方法的研究

基本信息

批准号：
13670912
负责人：
YASUOKA Kiyoshi
金额：
$ 2.18万
依托单位：
University of Tsukuba
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13670912/
关键词：
Proton Therapy Dose Distribution Range Distribution MonteCarlo Simulation Two Photon Events GEANT BGO モンテカルロシミュレーション二光子事象

项目摘要

Monte Carlo simulation of proton irradiation into a patient has been performed using CT data obtained for real proton treatment. We examined practical capability of this simulation method in treatment planning system in proton therapy in a point of calculation time, a model of secondary particle effects in proton irradiation, and possibility in use of dose distribution function produced with the Monte Carlo simulation. The GEANT is applied to the simulation in the proton therapy. It is a particle-based full simulation code including nuclear interaction. A patient structure is constructed with voxels, whose properties are determined by CT data. In the proton therapy, the simulation requires an atomic number Z and an atomic mass A of the material in each voxel. Thus an electron density in the CT data should be converted into Z and A in the proton simulation. Effective atomic number Z_<eff> and atomic mass A_<eff> are defined as : Z_<eff>=Σω_iZ_i, A_<eff>=Σω_iA_i, ω_i=P_iA_i/ΣP_iA_i, wher … More e P_i is a number weight of the i'th component in a material. They are expressed as a function of the CT data using calibration curves determined from phantom data. Each 5mm-thick slice of the CT data has 320×320 pixels in 1mm×1mm size. The patient structure is constructed as a group of voxels, as setup in the simulation code as planned in the treatment planning system. We developed the model with the following three points in the Monte Carlo simulation : (1) calculating energy deposit and kinematical parameter values once for a proton passing through each voxel, (2) making tables of spatial and kinematical distribution of only protons for each ridge filter and each proton energy in production at the front of compensator (bolus filter), and (3) using extended-depth-dose distribution in estimating energy deposits of primary and secondary protons passing through voxels. In introducing this model to the Monte Carlo simulation with the GEANT code, calculation time is 1-2 hours in producing dose distribution in a patient body under the following calculation condition : one PC workstation (Linux OS, Pentium4), 1% accuracy for each voxel cross-section of 1 slice (5mm×2mm), in a circle of 7cm in radius perpendicular to the proton beam at 250MeV. Independence of each event calculation in the Monte Carlo simulation makes it possible to reduce computing time 1/n with using n parallel sets of PC workstation. Clusterization of these PC workstation sets makes statistics n times easily in summing up events. We consider that this method is capable as treatment planning system in proton therapy, with several parallel sets of PC workstation. Less

蒙特卡罗模拟质子照射到一个病人已经进行了使用CT数据获得真实的质子治疗。我们检验了该模拟方法在质子治疗的治疗计划系统中在某一计算时间点的实用能力，质子辐照的二次粒子效应模型，以及使用蒙特卡罗模拟产生的剂量分布函数的可能性。将GEANT应用于质子治疗过程的模拟。它是一个基于粒子的完整模拟代码，包括核相互作用。患者结构由体素构成，体素的属性由CT数据确定。在质子治疗中，模拟需要每个体素中材料的原子序数Z和原子质量A。因此，CT数据中的电子密度应转换为质子模拟中的Z和A。有效原子序数Z_<eff>和原子质量A_<eff>定义为：Z_<eff>=Σω_iZ_i, A_<eff>=Σω_iA_i, ω_i=P_iA_i/ΣP_iA_i，其中…More e P_i为材料中第i个组分的数权值。它们被表示为使用从幻象数据确定的校准曲线的CT数据的函数。每个5mm厚的CT数据切片有320×320像素，尺寸为1mm×1mm。患者结构被构造为一组体素，在治疗计划系统中计划的模拟代码中设置。在蒙特卡罗模拟中，我们利用以下三点来开发模型：(1)一次计算质子通过每个体素的能量沉积和运动学参数值；(2)在补偿器（丸状过滤器）前部制作每个脊状过滤器和每个产生的质子能量的空间和运动学分布表；(3)使用扩展深度-剂量分布来估计通过体素的初级和次级质子的能量沉积。在用GEANT代码将该模型引入蒙特卡罗模拟时，计算时间为1-2小时，计算条件为：一台PC工作站（Linux操作系统，Pentium4），在垂直于250MeV质子束的半径为7cm的圆内，每片体素截面精度为1% （5mm×2mm）。蒙特卡罗模拟中每个事件计算的独立性使得使用n组并行PC工作站可以减少1/n的计算时间。这些PC工作站的集群化使得事件的统计容易进行n次汇总。我们认为该方法可以作为质子治疗的治疗计划系统，具有多台并行PC工作站。少