医用电子直线加速器治疗室的中子防护屏蔽设计

目的 研究治疗室内中子来源和中子散射的实质,分析计算加速器机房治疗室及迷路内中子剂量的变化规律,进行屏蔽设计。方法 本文基于对一台运行中的15MeV加速器治疗平面上关注点的中子通量测量结果,参考NCRP 79号报告,进行屏蔽防护设计和计算。结果 医用加速器产生X射线达到一定能量时,光核反应中子是医用加速器机房中子污染的主要来源。在加速器治疗室出入口处,主要的辐射防护是通过散射进入迷路内侧入口的杂散中子及其俘获γ辐射。结论 中子污染与治疗作用无关,但却给相关人员增加了额外剂量负担,一定条件下,也可能产生中子照射危害。所以,应重视医用加速器产生的中子外照射危害,对医用加速器治疗室内中子污染需进行防护设计和评价。

Design to neutron shielding for medical LINAC therapy room

Objective To study the source of neutron in the therapy room and the essence of neutron scattering,to analyze the change patten of neutron dose in the therapy room as well as in the maze so as to design the shielding.Methods Based on the measurement of the neutron flux for concerning points at the patient plane caused by a running 15 MeV accelerator and referred to NCRP report 79,this paper carried out the radiation protection design and calculation.Results When X-ray produced by medical accelerator reached certain energy,photonuclear reaction is the main source of neutron contamination in medical accelerator room.The main target of protection is the scattered neutron that comes to inside entrance of the maze and the γ-ray caused by them.As a result neutron contamination has nothing to do with the therapeutic effect,but only to increase the dose commitment for relevant person.Conclusions Neutron contamination has nothing to do with therapeutic effect,but only to increase the dose commitment for relevant person.Under certain conditions,it may also cause radiation insult to them.Therefore,certain attention should be paid the hazard caused by neutron external exposure,at the same time shielding design and evaluation should be implemented against the neutron contamination in medical accelerator room.