Varian Edge加速器射野外辐射剂量水平与铅防护用品的防护效果

目的:研究Varian Edge加速器不同工作状态下射野外辐射剂量水平以及铅防护用品的防护效果。方法:利用实验测量的方法，研究加速器在不同工作能量、不同线束均整状态、使用不同防护用品，测量距射野边缘不同距离及不同深度下辐射剂量水平的变化情况。结果:射野外辐射剂量随距射野边缘距离增加（5~40 cm）近似呈指数规律下降，距射野边缘20 cm范围内低能量射束（6 MV、6 MV FFF）的辐射剂量低于高能射束（10 MV、10 MV FFF）的辐射剂量，且随测量深度增加（1~2 cm）而降低。非均整模式下射野外剂量测量结果低于均整模式射束。在相同能量条件下，铅防护用品的防护效果与线束的均整状态无关。对高能射束的防护效果要优于低能射束且随深度增加防护效果迅速下降。深度为1 cm，射束能量10 MV FFF，距射野边缘5~30 cm条件下，防护效果最强，射野外辐射剂量水平降低50%以上。测量深度为2 cm，射束能量为6 MV FFF，距离射野边缘5~30 cm的条件下，防护效果最差，仅能降低10%以下。结论:在实现临床目标的前提下，治疗过程中若无铅防护用品进行保护，推荐采用低能非均整模式进行计划设计；若使用铅防护用品进行保护，可以采用高能非均整模式射束，此时铅防护用品效果最佳，射野外浅层器官所受剂量最低，可有效降低二次肿瘤发生几率。

Out-of-field dose distributions of different beams from Varian Edge accelerator and protection effects of lead protective equipments

Abstract: Objective To study the out-of-field dose distributions of different beams from Varian Edge accelerator under different working conditions and to investigate the protection effects of lead protective equipments. Methods When different energy levels, flattening filter-free (FFF) or flattening filter (FF) mode, and different protective equipments were adopted, the variations of the dose distributions at different distances from the edge of the beam field and at different depths of measurement were determined by experimental measurements. Results The out-of-field dose distributions were approximately exponentially decreasing with increasing distance from the edge of the beam field (5-40 cm). Within 20 cm from the edge of the beam field, the irradiation dose of low-energy beams (6 MV, 6 MV FFF) was lower than that of high-energy beams (10 MV, 10 MV FFF), and the irradiation dose was decreased with the increase of the depth of measurement (1-2 cm). FFF mode had more obvious effects on reducing the out-of-field dose distributions as compared with FF mode. Under the same energy condition, the protective effect of lead protective equipments was independent on FF or FFF mode. The protection against high-energy beams was better than that against low-energy beams, and the protective effect was decreased rapidly with the increase of the depth of measurement. When the depth of measurement was 1 cm, the protective effect was the strongest for the condition of 10 MV FFF beams and 5-30 cm from the edge of the beam field, and the reduction of out-of-field doses was larger than 50%. When the depth of measurement was 2 cm, the protective effect was the worst for the condition of 6 MV FFF beams and 5-30 cm from the edge of the beam field, and only a reduction of 10% was achieved. Conclusion Under the premise of achieving clinical goals, if no lead protective equipments were applied during the treatment, it is recommended to adopt low-energy FFF beams. If lead protective equipments were used for protection, high-energy FFF beams can be adopted, and at that time, the protective effect of lead protective equipments is the best, and the shallow organs out of the field are irradiated by the lowest dose, which can greatly reduce the probability of secondary cancer.