Analysis of radiation dose at the entrance of the medical linear accelerator treatment room

Abstract

Objective To investigate the radiation dose at the entrance of the accelerator treatment room, and to guide the radiation protection detection at the entrance of the treatment room.

Methods The FLUKA program was used to build the model of accelerator head and treatment room. Under the simulation conditions of 10 MV and 600 cGy/min for the accelerator, the radiation dose rate inside the entrance of the treatment room was measured at different gantry angles, irradiation conditions, and labyrinths.

Results The entrance dose rate with a water tank was significantly higher than that without a water tank under different inner labyrinth wall thicknesses and gantry angles. The entrance dose rate reached the maximum at the inner labyrinth wall thickness of 1 800 mm and the gantry angle of 90°. When the inner labyrinth wall thickness was 1 000 mm and the gantry angles were 0° and 180°, the entrance dose rate was significantly higher than that at other conditions. The dose rate at the entrance of the treatment room reached (82.26 ± 48.95) μSv/h to (314.09 ± 96.34) μSv/h under the following conditions: the inner labyrinth wall thickness of 1 800 mm, the gantry angle of 90°, with a water tank, and the width of the inner labyrinth entrance of 1 400-2 200 mm.

Conclusion The dose at the entrance of the accelerator treatment room mainly comes from the scattering and leakage radiation of the useful wire harness on the patient’s body surface, and the entrance dose rate increases with the increase in the width of the inner labyrinth entrance. In the entrance protection test, the gantry angle should be determined considering the inner labyrinth wall thickness, and the test should be performed at four angles in the uncertain case to ensure the comprehensiveness and accuracy of test results.

Abstract

摘要： 目的 探究加速器机房入口辐射剂量, 指导机房入口防护检测。 方法 利用 FLUKA 程序构建加速器机头及机 房模型, 模拟加速器在 10 MV 和 600 cGy/min 条件下, 比较不同机架角度、照射条件和迷路情况下机房入口内侧的辐 射剂量率。 结果 不同迷路内墙厚度和机架角条件下, 有水箱时入口剂量率明显大于无水箱情况。迷路内墙厚度为 1 800 mm, 机架角为 90°时入口剂量率最大。迷路内墙厚度为 1 000 mm, 机架角为 0°和 180°时, 入口剂量率明显大于 其他情况。迷路内墙为 1.80 m、机架角为 90°、有水箱、迷路内入口宽为 1 400~2 200 mm 时, 机房入口处剂量率在 (82.26 ± 48.95)～(314.09 ± 96.34) μSv/h。 结论 加速器机房入口处的剂量主要来自于有用线束在患者体表的散射和 泄漏辐射, 入口剂量率随迷路内口宽度递增。在入口防护检测时, 机架角度的选取要考虑迷路内墙厚度, 在不明确情 况下对 4 个角度进行检测, 保证检测结果的全面和准确。