Output dose investigation and analysis of external beam radiotherapy in Beijing

Objective To study the output dose of external beam radiotherapy in Beijing and analyze the cause of output dose deviation. Guidance is given on the selection of measurement methods, calculation formulas and parameters. Methods During 2020, the output doses of medical electron accelerators, tomotherapy, cyberknife, and γ-knife were measured based on the water absorbed dose calibration factor combined with the requirements in the IAEA TRS398 and TRS483 reports, and low-energy X-rays were measured based on the air kerma calibration factor combined with the requirements in the AAPM protocal. The output dose was measured and compared with the preset irradiation value. Results A total of 59 external beam radiation therapy equipments’s output dose were investigated. 2 of the 49 accelerators’s absolute value of relative deviation between the system indication value and the measurement exceeded 3%; the deviation of other external beam radiotherapy equipments was less than 3%. Conclusion A unified method and multi-party quality control can ensure the accuracy of the output dose. In the routine operation of the equipment, the hospital should strictly implement periodic inspections to ensure accurate and reliable radiotherapy. 摘要： 目的 调查北京地方所属外照射放射治疗设备输出剂量的情况, 分析输出剂量相对偏差原因, 明确测量方法、 计算公式及参数的选取。 方法 2020 年期间, 采用水中吸收剂量校准因子结合国际原子能机构 (IAEA) TRS398 和 TRS483 号报告中的要求对医用电子加速器、螺旋断层放射治疗装置、机械臂放射治疗装置、 γ 射线立体定向放射治疗 系统的输出剂量进行测量, 采用空气比释动能校准因子结合 AAPM 方案中的要求对低能 X 射线治疗机的输出剂量进 行测量, 并与预置照射值进行比较分析输出剂量相对偏差。 结果共调查了 59 台外照射放射治疗设备的输出剂量, 49 台医用电子加速器中 2 台输出剂量相对偏差绝对值超过 3%; 其他外照射放射治疗设备的输出剂量相对偏差绝对值 均小于 3%。 结论 统一明确的测量方法和多方的质量控制检测可确保放射治疗设备输出剂量的准确, 在设备常规运 行中医院应严格执行周期性检验保证实施精确可靠的放射治疗。