摘要
在硼中子俘获治疗(BNCT)装置中,束流整形体(BSA)的作用是将中子源产生的快中子束流慢化至超热中子能区(0.5 eV<E<10 keV),并尽可能减弱快中子、热中子和γ射线的成分,同时保证中子的方向性,其设计与优化是BNCT装置设计工作的核心内容之一.本文采用3.5 MeV,10 mA的质子束轰击锂靶,由核反应~7Li(p,n)~7Be产生的中子为源项,针对BSA的慢化体材料和结构、γ屏蔽层和热中子吸收层的厚度等参数进行蒙特卡罗模拟设计与优化.研究发现,采用Fluental和LiF两种慢化材料间隔2 cm层状堆叠的三明治BSA构型,在保证快中子剂量成分(D_f/φ_(epi)),γ剂量成分(D_γ/φ_(epi))和热中子比例φ_(th)/φ_(epi)满足IAEA-TECDOC-1223报告推荐要求的同时,在BSA出口处超热中子注量率优于单独使用Fluental和单独使用LiF的BSA设计.BSA出口处修正的Synder人头几何模型中的剂量分布计算结果显示:上述三明治构型的深度剂量分布与单独使用Fluental材料构型的结果基本相当,优于单独使用LiF构型,表明Fluental和LiF层状堆叠的三明治BSA构型是一种可行的BSA结构.
Boron neutron capture therapy（BNCT）is expected to be an effective method of improving the treatment results on malignant brain glioma and malignant melanoma,for which no successful treatment has been developed so far.The beam shaping assembly（BSA）of accelerator-based boron neutron capture therapy（A-BNCT）consists of a moderator,a reflector,gamma and thermal neutron shielding and a collimator.The BSA moderates the fast neutron produced in target to epithermal energy range.Design of BSA is one of the key jobs in BNCT project.An optimized study was conducted to design a beam shaping assembly for BNCT facility based on 3.5 MeV 10 mA radio-frequency quadrupole proton accelerator at Dongguan Neutron Science Center.In this simulation work,the neutron produced from the-7Li（p,n）-7Be reaction by 3.5 MeV proton is adopted as a neutron source term.In order to search for an optimized beam shaping assembly for accelerator-based BNCT,Monte Carlo simulation is carried out based on the parameters of moderator material and structure,the Gamma shielding,and the thermal neutron filter in the beam shaping assembly.The beam shaping assembly in this work consists of various moderator materials,teflon as reflector,Bi as gamma shielding,-6Li as thermal neutron filter,and lithium polyethylene as collimator.After comparing the simulation results of Fluental and LiF moderator materials,the beam shaping assembly configuration based on sandwich Fluental-LiF configuration is proposed.The sandwich Fluental-LiF configuration is made up of Fluental and LiF layer by layer,like a sandwich structure,and each layer is 2 cm thick.According to the beam quality requirement of the IAEA-tecdoc-1223report,the optimized epithermal neutron flux in air at the exit of BSA of the sandwich Fluental-LiF configuration is9.14×10-8n/（cm-2·s）,which is greater than those of the Fluental configuration（7.81×10-8n/（cm-2·s））and LiF configuration（8.79×10-8n/（cm-2·s））,when the ratio of fast neutron component to gamma ray component to thermal neutron is less than the limiting value of IAEA recommendation.Subsequently,the depth distribution of the equivalent doses in the Snyder head phantom is calculated to evaluate the treatment characteristic.The simulation results show that the therapy rate of the beam shaping assembly based on the sandwich Fluental-LiF configuration is basically equal to that of the Fluental configuration and better than that of the LiF configuration,and the therapy time is less than that of the Fluental configuration.This means that the beam shaping assembly based on the sandwich Fluental-LiF configuration is one of the suitable options for our accelerator-based BNCT.
作者
田永顺
胡志良
童剑飞
陈俊阳
彭向阳
梁天骄
Tian Yong-Shun;Hu Zhi-Liang;Tong Jian-Fei;Chen Jun-Yang;Peng Xiang-Yang;Liang Tian-Jiao(School of Physics and Optoelectronics,Xiangtan University,Xiangtan 411105,China;Dongguan Neutron Science Center,Dongguan 523803,China;Institute of High Energy Physics,Chinese Academy of Sciences,Beijing 100049,China)
出处
《物理学报》
SCIE
EI
CAS
CSCD
北大核心
2018年第14期119-126,共8页
Acta Physica Sinica
基金
国家重点研发计划(批准号:2016YFA0401504)
广东省产学研合作项目(批准号:2015B090901048)资助的课题~~
关键词
硼中子俘获治疗
蒙特卡罗模拟
束流整形体
慢化
noron neutron capture therapy
Monte Carlo simulation
beam shaping assembly
moderator
