Monte Carlo investigation of collimator scatter of proton-therapy beams produced using the passive scattering method
Monte Carlo investigation of collimator scatter of proton-therapy beams produced using the passive scattering method
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DOI：
10.1088/0031-9155/53/2/014
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发表时间：
2008-01-21
影响因子：
3.5
通讯作者：
Newhauser, Wayne D.
中科院分区：
文献类型：
--
作者：
Titt, Uwe;Zheng, Yuanshui;Newhauser, Wayne D.
当质子治疗束通过场限制孔径时，一些质子从准直器的边缘散射。边缘散射质子会降低患者或体模中的剂量分布，并且这些效应难以用诸如治疗计划系统中可用的分析方法来建模。这项工作的目的是量化边缘散射质子的剂量影响的各种临床治疗光束的代表性。使用蒙特卡罗模拟质子束从当代治疗设施的剂量影响进行了评估。质子束的特性是不同的，包括穿透范围（6.4-28.5 cm）、展开布拉格峰的宽度（SOBP; 2-16 cm）、射野大小（3 x 3 cm（2）至15 x 15 cm（2））和空气间隙，即准直器与体模之间的距离（8-48 cm）。模拟结果显示，边缘散射质子的剂量影响随着射程的增加而强烈增加（相对于在展开的布拉格峰的中心处的剂量，剂量增加6-20%），随着场尺寸的增加而强烈地降低（剂量变化2-20%），随着气隙的增加（剂量增加2-6%）适度增加，并且随着SOBP宽度的增加（剂量变化< 4%）微弱增加。在所研究的所有情况下，影响在浅水处最大。我们的结论是，边缘散射质子沉积的剂量可以扭曲的剂量近端的目标与不同的贡献，由于质子的范围，治疗领域的大小，准直器的位置和厚度，和宽度的SOBP。我们的研究结果还表明，准确预测每监测单位计算的剂量可能需要考虑从患者特定准直器的边缘散射的质子的剂量，特别是对于小的横向尺寸和深的深度的字段。
As a proton-therapy beam passes through the field-limiting aperture, some of the protons are scattered off the edges of the collimator. The edge-scattered protons can degrade the dose distribution in a patient or phantom, and these effects are difficult to model with analytical methods such as those available in treatment planning systems. The objective of this work was to quantify the dosimetric impact of edge-scattered protons for a representative variety of clinical treatment beams. The dosimetric impact was assessed using Monte Carlo simulations of proton beams from a contemporary treatment facility. The properties of the proton beams were varied, including the penetration range (6.4-28.5 cm), width of the spread-out Bragg peak (SOBP; 2-16 cm), field size (3 x 3 cm(2) to 15 x 15 cm(2)) and air gap, i.e. the distance between the collimator and the phantom (8-48 cm). The simulations revealed that the dosimetric impact of edge-scattered protons increased strongly with increasing range ( dose increased by 6-20% with respect to the dose at the center of the spread- out Bragg peak), decreased strongly with increasing field size ( dose changed by 2-20%), increased moderately with increasing air gap ( dose increased by 2-6%) and increased weakly with increasing SOBP width ( dose change < 4%). In all cases examined, the effects were largest at shallow depths. We concluded that the dose deposited by edge-scattered protons can distort the dose proximal to the target with varying contributions due to the proton range, treatment field size, collimator position and thickness, and width of the SOBP. Our findings also suggest that accurate predictions of dose per monitor-unit calculations may require taking into account the dose from protons scattered from the edge of the patient-specific collimator, particularly for fields of small lateral size and deep depths.