Site-specific range uncertainties caused by dose calculation algorithms for proton therapy
Site-specific range uncertainties caused by dose calculation algorithms for proton therapy
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DOI：
10.1088/0031-9155/59/15/4007
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发表时间：
2014-08-07
影响因子：
3.5
通讯作者：
Paganetti, H.
中科院分区：
文献类型：
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作者：
Schuemann, J.;Dowdell, S.;Paganetti, H.
本研究的目的是评估在质子治疗中引入特定部位范围裕度以取代当前通用裕度的可能性。此外，目标是研究使用当前的分析剂量计算方法降低边际的潜力。为了这个目的，我们调查的影响，复杂的病人的几何形状的分析剂量计算算法的能力，以准确地预测质子场的范围。剂量分布预测的分析的双光束算法进行了比较，使用蒙特卡罗（MC）模拟（TOPAS）。共分析了7个疾病部位（肝脏、前列腺、乳腺、髓母细胞瘤-脊柱、髓母细胞瘤-全脑、肺和头颈部）的508个被动散射治疗射野。在通过双射束和MC算法计算的二维远端剂量表面上进行逐体素比较，以获得90%剂量水平（R90）和50%剂量水平（R50）远端位置的每个射野的平均范围差和均方根偏差。还分析了远端衰减区域的平均剂量降解，定义为80%和20%剂量水平（R80-R20）远端位置之间的距离。所有范围均以水当量距离计算。考虑到总范围的不确定性和剂量计算本身的不确定性，我们能够推导出特定地点的估计值。对于肝脏，前列腺和全脑领域，我们的研究结果表明，减少目前使用的不确定性的利润率是可行的，即使没有引入MC剂量计算。我们建议肝脏和前列腺治疗的范围边界分别为2.8% + 1.2 mm，全脑治疗的范围边界分别为3.1% + 1.2 mm。另一方面，目前的利润似乎是不够的一些乳房，肺和头颈部的病人，至少如果使用一般。如果不进行病例特定调整，则乳腺、肺和头颈部治疗需要6.3% + 1.2 mm的通用边界。我们的结论是，目前使用的通用范围不确定性的利润率在质子治疗应重新定义的网站特定的，复杂的几何形状可能需要一个字段的具体调整。对于几何形状不均匀的患者，建议使用MC模拟对治疗计划进行常规验证。
The purpose of this study was to assess the possibility of introducing site-specific range margins to replace current generic margins in proton therapy. Further, the goal was to study the potential of reducing margins with current analytical dose calculations methods. For this purpose we investigate the impact of complex patient geometries on the capability of analytical dose calculation algorithms to accurately predict the range of proton fields. Dose distributions predicted by an analytical pencil-beam algorithm were compared with those obtained using Monte Carlo (MC) simulations (TOPAS). A total of 508 passively scattered treatment fields were analyzed for seven disease sites (liver, prostate, breast, medulloblastoma-spine, medulloblastoma-whole brain, lung and head and neck). Voxel-by-voxel comparisons were performed on two-dimensional distal dose surfaces calculated by pencil-beam and MC algorithms to obtain the average range differences and root mean square deviation for each field for the distal position of the 90% dose level (R90) and the 50% dose level (R50). The average dose degradation of the distal falloff region, defined as the distance between the distal position of the 80% and 20% dose levels (R80-R20), was also analyzed. All ranges were calculated in water-equivalent distances. Considering total range uncertainties and uncertainties from dose calculation alone, we were able to deduce site-specific estimations. For liver, prostate and whole brain fields our results demonstrate that a reduction of currently used uncertainty margins is feasible even without introducing MC dose calculations. We recommend range margins of 2.8% + 1.2 mm for liver and prostate treatments and 3.1% + 1.2 mm for whole brain treatments, respectively. On the other hand, current margins seem to be insufficient for some breast, lung and head and neck patients, at least if used generically. If no case specific adjustments are applied, a generic margin of 6.3% + 1.2 mm would be needed for breast, lung and head and neck treatments. We conclude that the currently used generic range uncertainty margins in proton therapy should be redefined site specific and that complex geometries may require a field specific adjustment. Routine verifications of treatment plans using MC simulations are recommended for patients with heterogeneous geometries.