用于碳离子束流布拉格峰展宽的新型多孔结构体的模拟  

Simulation of a new porous structure for Bragg peak broadening in carbon ion beam

作　　者：董思学 盛尹祥子 夏晓彬[1] DONG Sixue;SHENG Yinxiangzi;XIA Xiaobin(Shanghai Institute of Applied Physics,Chinese Academy of Sciences,Shanghai 201800,China;University of Chinese Academy of Sciences,Beijing 100049,China;Department of Medical Physics,Shanghai Proton and Heavy Ion Center,Shanghai 201321,China;School of Electronic Information and Electrical Engineering,Shanghai Jiao Tong University,Shanghai 201210,China)

机构地区：[1]中国科学院上海应用物理研究所,上海201800 [2]中国科学院大学,北京100049 [3]上海市质子重离子医院,上海201321 [4]上海交通大学电子信息与电气工程学院,上海201210

出　　处：《核技术》2022年第5期25-33,共9页Nuclear Techniques

基　　金：浦东新区科技发展基金(No.PKJ2019-Y08);上海市加强公共卫生体系建设三年行动计划(2020‒2022年)核医学与放射卫生学重点学科建设项目(No.E1902501)资助。

摘　　要：模拟了一种新型的多孔结构体(PS 2.0)用于展宽碳离子束流的布拉格峰。使用蒙特卡罗程序FLUKA建立了第一代波纹滤波器、PS 2.0和PS 1.0的几何模型,并比较了三者对束流的调制效果,包括展宽效果、束流均匀性和等中心束斑大小。结果显示:与PS 1.0相比,经PS 2.0展宽后的碳离子束流后沿半影宽度减少了最多1.11 mm;使用PS 2.0调制后的束流具有良好的均匀性;在相同射程深度下,当PS 2.0与等中心位置之间的距离小于10 cm时,使用PS 2.0后的等中心束斑最多减少了1.72 mm(13.93%)。表明PS 2.0能够在展宽布拉格峰的同时兼顾后沿半影的宽度,保证了调制后束流的均匀性,并在一定程度上减小了等中心束斑的大小。[Background]In particle radiotherapy,the Bragg peak(BP)width of carbon ion beam is required to be broadened whilst Ripple filter(RiFi)is often used as a clinical broadening device.However,it may cause extra lateral scattering.Porous material expressed as the porous structure 1.0(PS 1.0)can be used to reduce such scattering but bring an oversized distal falloff width(DFW).[Purpose]This study aims to develop a novel porous structure,described as a porous structure 2.0(PS 2.0),to broaden the BP width.[Methods]First of all,the Monte Carlo code,FLUKA was selected as the tool for this simulation.Two geometry models of broadening structure(1D-RiFi and PS 1.0)were built.Then,the PS 2.0 was simulated by inserting numerous of Polymethyl Methacrylate(PMMA)sticks in the PS 1.0 with a certain proportion.The performance of PS 2.0 was evaluated by analyzing the DFW and isocenter spot size of the modulated carbon ion beams.Finally,a plane homogeneous radiation field was simulated and fluence homogeneities were compared by using a 2D(X-Z)dose distribution and quantized by calculating the 1D-lateral flatness.[Results]Compared to the PS 1.0,the DFW is reduced by at most 1.11 mm by using PS 2.0 with a similar BP width broadening ability at the same beam range.Fluence homogeneity of PS 2.0 is excellent in all the downstream locations,and the isocenter spot size is reduced by at most 1.72 mm at the same beam range.[Conclusions]This study provides a new method for simulating the PS 2.0 as a BP broadening device with smaller DFW,better homogeneous and reduced isocenter spot size in comparison to PS 1.0.

关 键 词：蒙特卡罗模拟 点扫描碳离子束流 多孔结构 布拉格峰 波纹滤波器 

分 类 号：TL8[核科学技术—核技术及应用]