质子治疗工作场所屏蔽计算方法的探讨

目的 探讨质子治疗工作场所屏蔽计算方法，为质子治疗工作场所的设计和现有国家标准的完善提供科学依据。方法 采用国家标准和国内外文献提供的计算公式及关键特征参数，结合基于蒙特卡罗方法的FLUKA对质子治疗工作场所屏蔽体外关注点的中子周围剂量当量率进行经验公式计算和蒙特卡罗模拟，分析2种方法的估算结果。结果 相对于发散狭缝束流损失点0°和50° 2个方向上单指数公式计算结果（0.13、12.4），双指数公式计算结果（0.40、17.9）与蒙特卡罗模拟结果（0.32 ±0.19、18.2 ±4.98）的符合性更好；铜靶和镍靶蒙特卡罗模拟结果基本一致，可以认为铜靶的混凝土屏蔽关键特征参数可较好地应用于镍靶计算过程，但当用于钽靶时会低估中子周围剂量当量率，0°和40° 2个方向上相差分别为5.7倍和1.3倍。结论 依据国内外文献中计算公式及关键特征参数得到的剂量率估算值与FLUKA模拟结果具有较好的符合性，可作为现有国家标准的补充和完善应用于质子治疗工作场所屏蔽设计。

Discussion on shielding calculation method for proton therapy room

Objective To discuss the shielding calculation method for proton therapy room, and to provide a scientific basis for shielding design of proton therapy room and improvement of existing national standards. Methods Using the calculation formula and key characteristic parameters from national standards and Chinese and foreign literature, combining with the FLUKA Monte Carlo method, empirical formula calculation and Monte Carlo simulation were conducted for the neutron ambient dose equivalent rates of the focuses outside the shielding of proton therapy room. The estimation results of the two methods were analyzed. Results Relative to the calculation results of the single exponential formula in the two directions of 0° and 50° in the beam loss point of divergence slit (0.13 and 12.4), the calculation results of the double exponential formula (0.40 and 17.9) were more consistent with the Monte Carlo simulation results (0.32 ±0.19 and 18.2 ±4.98). The Monte Carlo simulation results of copper target and nickel target were similar, suggesting that the key characteristic parameters of concrete shielding for copper target could be well applied to the calculation of nickel target, but the neutron ambient dose equivalent rates were underestimated when applied to tantalum target, with a difference of 5.7 times and 1.3 times in the two directions of 0° and 40°, respectively. Conclusion The dose rate estimates based on the calculation formula and key characteristic parameters from Chinese and foreign literature are consistent with FLUKA simulation results, and this method can be used in the shielding design of proton therapy room as a supplement and improvement to the existing national standards.