立体定向伽玛射线放射治疗机房屏蔽计算分析

Analysis and calculation of the shielding enclosure in gamma ray stereotactic radiotherapy room

目的通过对某医院即将投入使用的立体定向伽玛射线放射治疗机房的屏蔽进行屏蔽计算,保证其剂量学参数和防护安全性能符合相关标准和要求。方法根据《X、γ射线头部立体定向外科治疗放射卫生防护标准》(GBZ 168-2005)等标准,运用不同的方法进行验证计算:方法一按照剂量管理控制值对选取的六个关注点进行验证计算;方法二根据治疗室剂量场分布情况,治疗室墙体外30 cm可达界面处因透射产生的空气比释动能率一般应不大于2.5μSv/h,对选取的六个关注点进行验证计算。同时计算防护门的防护厚度。采用综合厚度原则给出最终屏蔽的综合厚度,并结合建设单位设计结果进行了验证。结果本文立体定向伽玛射线放射治疗系统机房屏蔽的防护设计厚度大于计算结果,用于屏蔽泄露辐射和患者散射的各墙体设计厚度均为0.8 m,材料为混凝土,迷路外墙设计厚度为0.45 m,材料为混凝土,铅体防护门设计厚度为15 mm。结论本文立体定向伽玛射线放射治疗系统机房屏蔽的设计厚度符合要求。

Objective We conducted the shielding calculation for the shielding enclosure of the gamma ray stereotactic radiotherapy room,which was put into use in the hospital,aiming to ensure that the dosimetric parameters and safety performance could comply with the relevant requirements and standards.Methods According to《Radiological protection standards of X、(γ)-ray stereotactic radiosurgery for head treatment》(GBZ 168-2005),the shielding calculation was carried out and verified by using different analytical methods.Method 1 was to perform calculations for the selected six focus positions based on dose management control value.Method 2 was to perform verification for the selected six focus positions according to the dose field distribution of the treatment room,of which air kerma rate because of transmission at the 30 cm reachable interface outside the treatment room wall should not be greater than 2.5μSv/h,meanwhile,the protective thickness of protective door was calculated.The final comprehensive thickness of the shielding enclosure was defined by adopting comprehensive thickness principle,and that was verified with the design results of the development organization.Results In this study,the protective design thickness of the shielding enclosure of the gamma ray stereotactic radiotherapy room was greater than the calculated results.The design thickness of walls with concrete material reached 0.8 m to attenuate leakage radiation and patient scattering.The thickness of concrete maze exterior walls was 0.45 m.The design thickness of lead protective door was 15 mm.Conclusion The design thickness of the shielding enclosure of the gamma ray stereotactic radiotherapy room meets the requirements.