某医院M6型射波刀系统机房辐射屏蔽改造问题探讨

Discussion on reconstruction of radiation shield of M6 type radioknife system room in a hospital

目的探讨某医院M6型射波刀系统机房的辐射屏蔽问题。方法M6型射波刀系统输出6 MV X射线,剂量率1000 MU/min,射线泄漏辐射因子≤0.1%,最大上仰角18°。依据GBZ/T 201.2—2011《放射治疗机房的辐射屏蔽规范第2部分:电子直线加速器放射治疗机房》(以下简称“GBZ/T 201.2—2011”)、NCRP 151号报告《兆伏级X、γ射线放射治疗设施机房屏蔽防护设计与评价》、英国现行电离辐射法规(Ionising Radiations Regulations 2017,以下简称“IRR 17”)推荐的计算方法,基于3种方法推荐的不同的剂量率控制水平估算机房所需的屏蔽墙体厚度,并与现有机房情况进行比较。结果①参照中国GBZ/T 201.2—2011标准、美国NCRP 151报告以及英国现行IRR 17法规推荐的计算方法,得到各关注点A、B、C、D、E、F、G、H、L、M1/M2所需的混凝土厚度分别为224.08、193.42、205.97、205.65、224.53、194.79、144.97、177.17、79.78、71.89 cm,105.34、99.94、114.33、106.77、118.91、95.92、71.51、86.16、95.02、85.47 cm,122.59、116.25、135.72、124.03、136.17、113.17、84.33、102.04、112.28、100.26 cm。②与国外两种方法相比,基于GBZ/T 201.2—2011方法计算四周所需的屏蔽墙厚度最大,其原因是为保障放射工作人员及周围公众的安全,我国职业卫生标准对机房外周围剂量当量率的控制水平要求较严格所致。结论①加速器机房改造为射波刀机房应充分考虑射波刀的技术特点,必要时可适当增加原加速器机房次屏蔽墙体的厚度。②机房防护改造应综合考虑屏蔽材料种类、所需厚度、施工难度等具体情况,在条件允许的情况下,可在机房墙外进行屏蔽补偿,以保证机房内的有效使用面积。

Objective To discuss radiation shielding problem of the M6 CyberKnife Robotic Radiosurgery System room in a hospital.Methods To discuss M6 wave knife system outputs 6 MV X-ray,dose rate 1000MU/min,radiation factor of ray leakage≤0.1%,and maximum elevation angle 18.According to the dose estimation method recommended by GBZ/T 201.2-2011,<Radiation shielding standard for radiotherapy room:Part 2:Radiotherapy room of electron linear accelerator>(hereinafter referred to as"GBZ/T 201.2-2011")、NCRP report No.151.<Shielding design and evaluation of radiation therapy facility room for megavolt class X>and current UK ionizing radiation regulations(Ionising Radiations Regulations 2017,hereinafter referred to as"IRR17"),the thickness of shielding wall required for machine rooms based on different dose rate control levels recommended by the three methods were estimated,and the existing machine rooms were compared.Results@Using the calculation method recommended by the Chinese GBZ/T 201.2—2011 standard,the NCRP 151 report of the United States and the current IRR 17 regulations of the United Kingdom respectively,the concrete thickness required for each concern point A、B、C、D、E、F、G、H、L and M1/M2 were 224.08,193.42,205.97,205.65,224.53,194.79,144.97,177.17,79.78,71.89 cm;105.34,99.94,114.33,106.77,118.91,95.92,71.51,86.16,95.02,85.47cm;122.59,116.25,135.72,124.03,136.17,113.17,84.33,102.04,112.28,100.26 cm.②Compared with the two foreign methods,the thickness of the surrounding shielding wall calculated based on GBZ/T 201.22011 method is the largest,The reason is that in order to ensure the safety of radiation workers and the surrounding public,Chinas occupational health standards have relatively strict requirements on the control level of dose equivalent rate outside the machine room.Conclusion The technical characteristics of the wave knife should be fully considered when the accelerator room is transformed into the wave knife room,and the thickness of the secondary shielding wall of the original accelerator room can be appropriately increased if necessary.②The protection transformation of the machine room shall comprehensively consider the specific conditions such as the type of shielding materials,the required thickness,and the construction difficulty.If conditions permit,shielding compensation can be carried out outside the machine room wall to ensure the effective use area in the machine room.