Titt U, Newhauser W D
Department of Radiation Physics, The University of Texas M D Anderson Cancer Center, 1515 Holcombe Boulevard, Unit 94, Houston, TX 77030, USA.
Radiat Prot Dosimetry. 2005;115(1-4):144-8. doi: 10.1093/rpd/nci252.
Proton therapy facilities are shielded to limit the amount of secondary radiation to which patients, occupational workers and members of the general public are exposed. The most commonly applied shielding design methods for proton therapy facilities comprise semi-empirical and analytical methods to estimate the neutron dose equivalent. This study compares the results of these methods with a detailed simulation of a proton therapy facility by using the Monte Carlo technique. A comparison of neutron dose equivalent values predicted by the various methods reveals the superior accuracy of the Monte Carlo predictions in locations where the calculations converge. However, the reliability of the overall shielding design increases if simulation results, for which solutions have not converged, e.g. owing to too few particle histories, can be excluded, and deterministic models are being used at these locations. Criteria to accept or reject Monte Carlo calculations in such complex structures are not well understood. An optimum rejection criterion would allow all converging solutions of Monte Carlo simulation to be taken into account, and reject all solutions with uncertainties larger than the design safety margins. In this study, the optimum rejection criterion of 10% was found. The mean ratio was 26, 62% of all receptor locations showed a ratio between 0.9 and 10, and 92% were between 1 and 100.
质子治疗设施设有防护措施，以限制患者、职业工作人员和普通公众所接触的二次辐射量。质子治疗设施最常用的屏蔽设计方法包括估算中子剂量当量的半经验法和分析法。本研究通过使用蒙特卡罗技术，将这些方法的结果与质子治疗设施的详细模拟结果进行比较。对各种方法预测的中子剂量当量值进行比较后发现，在计算收敛的位置，蒙特卡罗预测的准确性更高。然而，如果可以排除因粒子历史记录过少等原因导致解未收敛的模拟结果，并在这些位置使用确定性模型，则整体屏蔽设计的可靠性会提高。在这种复杂结构中接受或拒绝蒙特卡罗计算的标准尚未得到很好的理解。一个最佳的拒绝标准应能考虑到蒙特卡罗模拟的所有收敛解，并拒绝所有不确定性大于设计安全裕度的解。在本研究中，发现最佳拒绝标准为10%。平均比值为26，62%的所有受体位置的比值在0.9至10之间，92%在1至100之间。
