Evaluation on radiation shielding of the Halcyon linear accelerator room in a hospital

Abstract

Objective To explore the radiation shielding problem of Halcyon linear accelerator room.

Methods According to the dose estimation method recommended by GBZ/T 201.2—2211 Radiation Shielding Requirements for Radiotherapy room—Part 2: Radiotherapy Room of Electron Linear Accelerators (hereinafter referred to as GBZ/T 201.2—2211) and NCRP report No. 151 Structural Shielding Design and Evaluation for Megavoltage X- and Gamma-Ray Raaiotherapy Facilities the required shielding thickness of 6.0 MeV Halcyon linear machine room is evaluated and compared with the existing machine room. After the equipment was put into use, we measured and verified the dose equivalent rate around each point.

Results i) The transmittance of the main beam passing through the self-shielding system was 0.06%. The theoretical shielding thickness of the main beam path sites A, C and L of the accelerator (two main shielding walls and room top sites respectively) was 136.00, 130.00 and 136.00 cm, which was lower than the required shielding thickness of the main shielding area specified in GBZ/T 201.2—2011 for 6.0 MeV accelerator. ii) Compared with the existing equipment rooms in the hospital, except that the thickness of the top secondary shield (80.00 cm) and the thickness of the west section of the outer wall of the labyrinth (100.00 cm) are smaller, the rest meets the shielding requirements. iii) After the transformation of the computer room and the installation of Halcyon linear accelerator, the surrounding dose equivalent rate was lower than the control level required by GBZ/T 201.2—2011.

Conclusion The self-shielding design of Halcyon linear accelerator can effectively protect 6.0 MeV rays used for treatment, reduce the shielding thickness required for the main shielding area, reduce the shielding construction cost of the equipment room and increase the usable area of the equipment room.

Abstract

摘要： 目的 探讨 Halcyon 直线加速器机房的辐射屏蔽问题。 方法 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”) 和美国国家辐射防护和测量委员 会 151 号报告推荐的剂量估算方法, 估算某医院 6.0 MeV Halcyon 直线加速器机房所需屏蔽厚度, 与现有机房情况进行比 较。设备投人使用后, 对各位点周围剂量当量率进行测量验证。 结果 (1) 主射束贯穿自屏蔽系统透射率为 0.06%, 加 速器主射束路径位点 A、C、L (分别为两主屏蔽墙和室顶位点)的理论屏蔽厚度分别为 136.00、30.00 和 136.00 cm, 均低 于 GBZ/T 201.2—2011 中 6.0 MeV 加速器规定的主屏蔽区所需屏蔽厚度。(2) 机房屏蔽设计估算结果与医院现有机房 情况比较, 除顶部次屏蔽厚度 (80.00 cm)、迷道外墙西段厚度 (100.00 cm) 偏小外, 其余均可满足屏蔽要求。(3) 机房改 造、Halcyon 直线加速器安装完成后, 加速器工作场所周围各位点的周围剂量当量率均小于 GBZ/T 201.2—2011 要求的控 制水平。 结论 Halcyon 直线加速器的自屏蔽设计可对治疗用的 6.0 MeV 射线进行有效防护;这有利于降低主屏蔽区所 需屏蔽厚度, 降低机房屏蔽建设成本, 提高机房使用面积。