后装γ源近距离治疗室内辐射场剂量水平及分布

Dose level and distribution of radiation field in a γ-ray source after loading brachytherapy room

目的掌握后装γ源近距离治疗室(简称后装治疗室)内辐射场剂量水平及其分布,为机房的防护设计和改造以及现场人员的放射防护指导提供科学决策。方法以北京市某医院1台RL-HZJ 18型192Ir后装γ源近距离治疗机(后装机)及其治疗室为研究对象,在实际放射源活度为254.7 GBq的情况下,使用AT1121型辐射巡测仪分别测量后装机贮源状态下治疗室内辐射场剂量水平和出束状态下迷路的剂量分布;使用热释光剂量计(TLD)测量患者治疗期间治疗室内关注点的辐射剂量水平。结果后装机贮源状态下距离设备表面5和100 cm处的周围剂量当量率最高值分别为24.0和0.56μSv/h;照射状态下迷路拐口周围剂量当量率为5.4×10~3μSv/h,相应的辐射比率为3.8×10^(-2),迷路内接近入口防护门处为9.4μSv/h,相应的辐射比率为6.8×10^(-5);患者治疗期间治疗室内墙面关注点的辐射比率为(0.235~201.4)×10^(-6)。结论后装治疗室迷路具有明显的防护效果,迷路的设置和治疗室内辐射剂量水平的实时监测是必要的。

[Objective] To know the dose levels and distribution of radiation field in a γ-ray source after loading brachytherapy room （brachytherapy room）, provide scientific decision-making for the radiation protection design and reconstruction of brachytherapy room and the guideline on radiological protection of radiotherapy onsite staff. [Methods] A 192Ir brachytherapy equipment typed with RL-HZJ 18 （brachytherapy equipment） and its room of a hospital were selected as the research objects. Under the condition of the actual source activity 254.7 GBq loaded in the equipment, the dose levels of radiation field in the room were measured with a radiation survey instrument typed AT1121 while the source being in stored state, and the dose distribution along maze were measured while the source being in exposure state. Radiation dose levels of the concerned points in the room were also measured accumulatively using thermoluminescence dosimeter （TLD） during the period of normal clinic treatment of patients. [Results] Under the condition of non-irradiation state, the maximum values of ambient dose equivalent rate around 5 and 100 cm away from the surface of the brachytherapy equipment were 24.0 and 0.56 μSv/h respectively. While the brachytherapy radioactive source was being in irradiation state, ambient dose equivalent rate measured on the maze turning place was 5.4×10^3 μSv/h which corresponding radiation ratio of 3.8×10^-5, and the ambient dose equivalent rate along the maze near entrance of the room was 9.4 μSv/h which corresponding radiation ratio of 6.8×10^-5. The radiation ratio of the concerned points on the wall surface in the room were in the range of （0.235-201.4）×10^-6. [Conclusion] It is shown that the maze of a brachytherapy room can develop obvious protective effect, and it is necessary that maze should be set and radiation levels in a brachytherapy room should be monitored in real-time.