Oregon Health and Science University, Portland, OR, United States of America. Oregon State University, Corvallis, OR, United States of America.
Phys Med Biol. 2018 Aug 6;63(15):15NT04. doi: 10.1088/1361-6560/aad1bc.
The purpose of this study was to independently apply an analytical model for equivalent dose from neutrons produced in a passive-scattering proton therapy treatment unit, H. To accomplish this objective, we applied the previously-published model to treatment plans of two pediatric patients. Their model accounted for neutrons generated by mono-energetic proton beams stopping in a closed aperture. To implement their model to a clinical setting, we adjusted it to account for the area of a collimating aperture, energy modulation, air gap between the treatment unit and patient, and radiation weighting factor. We used the adjusted model to estimate H per prescribed proton absorbed dose, D , for the passive-scattering proton therapy beams of two children, a 9-year-old girl and 10-year-old boy, who each received intracranial boost fields as part of their treatment. In organs and tissues at risk for radiation-induced subsequent malignant neoplasms, T, we calculated the mass-averaged H, H , per D . Finally, we compared H /D values to those of previously-published Monte Carlo (MC) simulations of these patients' fields. H /D values of the adjusted model deviated from the MC result for each organ on average by 20.8 ± 10.0% and 44.2 ± 17.6% for the girl and boy, respectively. The adjusted model underestimated the MC result in all T of each patient, with the exception of the girl's bladder, for which the adjusted model overestimated H /D by 3.1%. The adjusted model provided a better estimate of H /D than the unadjusted model. That is, between the two models, the adjusted model reduced the deviation from the MC result by approximately 37.0% and 46.7% for the girl and boy, respectively. We found that the previously-published analytical model, combined with adjustment factors to enhance its clinical applicability, predicted H /D in out-of-field organs and tissues at risk for subsequent malignant neoplasms with acceptable accuracy. This independent application demonstrated that the analytical model may be useful broadly for clinicians and researchers to calculate equivalent dose from neutrons produced externally to the patient in passive-scattering proton therapy.
本研究的目的是独立应用一种分析模型来计算被动散射质子治疗单元 H 中产生的中子的等效剂量。为了实现这一目标，我们将先前发表的模型应用于两名儿科患者的治疗计划。他们的模型考虑了停留在封闭孔径中的单能质子束产生的中子。为了将其模型应用于临床环境，我们对其进行了调整，以考虑准直孔径的面积、能量调制、治疗单元与患者之间的气隙以及辐射权重因子。我们使用调整后的模型来估计两名儿童（一名 9 岁女孩和一名 10 岁男孩）的被动散射质子治疗束每吸收质子剂量 D 时的 H，他们都接受了颅内加量照射作为治疗的一部分。在存在辐射诱导继发恶性肿瘤风险的器官和组织 T 中，我们计算了每吸收剂量 D 时的质量加权平均 H。最后，我们将 H /D 值与这些患者的场的先前发表的蒙特卡罗（MC）模拟结果进行了比较。调整后的模型的 H /D 值平均比每个器官的 MC 结果低 20.8±10.0%和 44.2±17.6%，分别为女孩和男孩。在每个患者的所有 T 中，除了女孩的膀胱，调整后的模型均低估了 MC 结果，而对于女孩的膀胱，调整后的模型高估了 H /D 约 3.1%。调整后的模型比未经调整的模型提供了更好的 H /D 估计值。也就是说，在这两种模型中，调整后的模型使女孩和男孩的 MC 结果的偏差分别降低了约 37.0%和 46.7%。我们发现，经过修正以增强其临床适用性的先前发表的分析模型，可以以可接受的精度预测出场外危及后续恶性肿瘤的器官和组织中的 H /D。这种独立应用表明，该分析模型可能对临床医生和研究人员广泛有用，可用于计算被动散射质子治疗中患者体外产生的中子的等效剂量。
