Impact of Spot Size and Spacing on the Quality of Robustly Optimized Intensity Modulated Proton Therapy Plans for Lung Cancer
Impact of Spot Size and Spacing on the Quality of Robustly Optimized Intensity Modulated Proton Therapy Plans for Lung Cancer
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DOI：
10.1016/j.ijrobp.2018.02.009
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发表时间：
2018-06-01
影响因子：
7
通讯作者：
Liu, Wei
中科院分区：
文献类型：
--
作者：
Liu, Chenbin;Schild, Steven E.;Liu, Wei
目的：为了研究光斑大小和间距如何影响稳健优化的强度调制质子治疗（IMPT）对肺癌的计划质量、稳健性和相互作用效应。方法和材料Z为10名肺癌患者创建了两个稳健优化的IMPT计划：首先通过大光斑机器在等中心处具有空气能量依赖的大光斑大小。（σ：6-15 mm）和间距（1.3 σ），第二次通过具有空气中能量依赖性小光斑尺寸（σ：2-6 mm）和间距（5 mm）的小光斑机器。两个计划都是通过使用内部开发的IMPT计划系统优化平均四维计算机断层扫描的内部靶体积的辐射剂量来生成的。使用剂量-体积直方图带方法来评估计划的稳健性。开发了剂量评价软件，以模拟时间依赖性点给药，从而将相互作用效应与每个部分每个射野的随机起始阶段结合起来。通过可变形图像配准对患者解剖体素进行逐相映射，并使用内部开发的软件对剂量进行评分。剂量体积直方图指数，包括内部靶体积剂量覆盖率，均匀性，和器官的风险（OARs）sparing，进行了比较，使用Wilcoxon符号秩检验。结果：与大点机相比，小点机导致心脏和食管的平均剂量显着降低，具有可比的目标剂量覆盖率，均匀性，和其他OARs的保护。目标和大多数OAR的计划稳健性相当。考虑到相互作用的影响，显着降低心脏和食管的平均剂量与可比的目标剂量覆盖率和均匀性，观察到使用较小的spots.Conclusions：稳健的优化与一个小斑点机器显着提高心脏和食管的保留，与计划的稳健性和相互作用的影响相比，稳健的优化与一个大斑点机器。与大光斑机器相比，小光斑机器使用更多数量的光斑来覆盖相同的肿瘤，这使得规划系统更自由地补偿对肺癌治疗的不确定性和相互作用效应的更高灵敏度。(C)2018爱思唯尔公司All rights reserved.
Purpose: To investigate how spot size and spacing affect plan quality, robustness, and interplay effects of robustly optimized intensity modulated proton therapy (IMPT) for lung cancer.Methods and MaterialsZ Two robustly optimized IMPT plans were created for 10 lung cancer patients: first by a large-spot machine with in-air energy-dependent large spot size at isocenter (sigma: 6-15 mm) and spacing (1.3 sigma), and second by a small-spot machine with in-air energy-dependent small spot size (sigma: 2-6 mm) and spacing (5 mm). Both plans were generated by optimizing radiation dose to internal target volume on averaged 4-dimensional computed tomography scans using an in-house-developed IMPT planning system. The dose-volume histograms band method was used to evaluate plan robustness. Dose evaluation software was developed to model time-dependent spot delivery to incorporate interplay effects with randomized starting phases for each field per fraction. Patient anatomy voxels were mapped phase-to-phase via deformable image registration, and doses were scored using in-house-developed software. Dose-volume histogram indices, including internal target volume dose coverage, homogeneity, and organs at risk (OARs) sparing, were compared using the Wilcoxon signed-rank test.Results: Compared with the large-spot machine, the small-spot machine resulted in significantly lower heart and esophagus mean doses, with comparable target dose coverage, homogeneity, and protection of other OARs. Plan robustness was comparable for targets and most OARs. With interplay effects considered, significantly lower heart and esophagus mean doses with comparable target dose coverage and homogeneity were observed using smaller spots.Conclusions: Robust optimization with a small spot-machine significantly improves heart and esophagus sparing, with comparable plan robustness and interplay effects compared with robust optimization with a large-spot machine. A small-spot machine uses a larger number of spots to cover the same tumors compared with a large-spot machine, which gives the planning system more freedom to compensate for the higher sensitivity to uncertainties and interplay effects for lung cancer treatments. (C) 2018 Elsevier Inc. All rights reserved.