Using field size factors to characterize the in-air fluence of a proton machine with a range shifter.
Using field size factors to characterize the in-air fluence of a proton machine with a range shifter.
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DOI：
10.1186/s13014-017-0783-2
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发表时间：
2017-03-14
期刊：
影响因子：
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通讯作者：
Bues M
中科院分区：
文献类型：
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作者：
Shen J;Lentz JM;Hu Y;Liu W;Morales DH;Stoker JB;Bues M
量程移位器 (RS) 用于治疗质子笔形束扫描系统 (PBS) 的浅层肿瘤。添加 RS 肯定会使治疗计划系统 (TPS) 的调试变得复杂，因为 RS 显着扩大了光斑尺寸。在这项工作中，我们提出了一种为具有固定 RS 的 PBS 系统配置商业 TPS 的有效方法。通过将螺旋输送与定制控制点相结合，我们能够显着提高测量效率，并在三小时内获得 250 个场尺寸因子 (FSF)。测量的 FSF 用于表征质子注量并拟合 TPS 中使用的双高斯注量模型的参数。使用在空气和水中测量的 FSF、扩散布拉格峰 (SOBP) 场的绝对剂量以及针对患者特定质量保证 (QA) 进行的剂量测量进行了广泛的验证。对于所有 250 个 FSF，测量的空中 FSF 与模型的预测一致在 3% 以内，而对于 94% 的 FSF 与模型的预测一致在 2 以内。对于空气中和水中的 FSF 以及 SOBP 光束的绝对剂量，模型的预测和测量之间的一致性在 2% 以内。 113 个视野的患者特异性 QA 显示出与 2 mm 和 2% 的伽马标准进行绝对剂量比较时出色的伽马通过率 (96.95±2.51%)。模型的预测和测量之间的良好一致性证明了所提出的使用 FSF 来表征质子注量并为具有固定 RS 的 PBS 系统配置 TPS 的方法的效率和准确性。
The range shifter (RS) is used to treat shallow tumors for a proton pencil beam scanning system (PBS). Adding RS certainly complicates the commissioning of the treatment planning system (TPS) because the spot sizes are significantly enlarged with RS. In this work, we present an efficient method to configure a commercial TPS for a PBS system with a fixed RS. By combining a spiral delivery with customized control points, we were able to significantly improve measurement efficiency and obtain 250 field size factors (FSF) within three hours. The measured FSFs were used to characterize the proton fluence and fit the parameters for the double-Gaussian fluence model used in the TPS. Extensive validation was performed using FSFs measured in air and in water, absolute doses of spread-out Bragg peak (SOBP) fields, and the dose measurements carried out for patient-specific quality assurance (QA). The measured in-air FSFs agreed with the model’s prediction within 3% for all 250 FSFs, and within 2 for 94% of the FSFs. The agreement between model’s prediction and measurement was within 2% for the in-air and in-water FSFs and the absolute doses for SOBP beams. The patient-specific QA of 113 fields showed an excellent gamma passing rates (96.95 ± 2.51%) for the absolute dose comparisons with gamma criteria of 2 mm and 2%. The excellent agreement between the model’s prediction and measurements proved the efficiency and accuracy of the proposed method of using FSFs to characterize the proton fluence and configure the TPS for a PBS system with fixed RS.