Experimental validation of a deforming grid 4D dose calculation for PBS proton therapy
Experimental validation of a deforming grid 4D dose calculation for PBS proton therapy
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DOI：
10.1088/1361-6560/aaad1e
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发表时间：
2018-03-01
影响因子：
3.5
通讯作者：
Zhang, Ye
中科院分区：
文献类型：
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作者：
Krieger, Miriam;Klimpki, Grischa;Zhang, Ye
本研究的目的是通过与测量值相比的4D剂量计算（4DDC）验证估计剂量分布的时间准确性。将针对肝脏患者病例（CTV体积：403 cc）优化的单野计划（0.6戈伊）输送到均质PMMA体模，并通过高分辨率双CCD系统在两个水等效深度处进行测量。使用4D Quasar体模模拟各种运动场景（无运动和振幅为10 mm的运动以及两个周期：3.7 s和4.4 s），并通过光学跟踪系统实时记录。应用了三种运动缓解方法（单次输送、6x分层和体积重新扫描），获得了10次单独测量。通过考虑包含实际输送光斑位置、注量和时间戳信息的输送日志文件（回顾性），在水中回顾性计算4D剂量分布。此外，为了评估4DDC输入的灵敏度，使用点递送和重复的周期性运动模式的估计时间戳来执行相应的预期4DDC作为比较。使用2D伽马分析和剂量差异直方图来量化测量值与最大计算剂量>5%的所有像素的计算值之间的一致性。结果表明，对于3%/3 mm标准，平均伽马评分为99.2%，标准差为1.0%，所有场景的评分均超过95%。剂量差异大于5%的平均面积为6.2%。由于输入不确定性而导致的偏差对于单次扫描交付是明显的，但一旦应用重新扫描，则可能会模糊不清。因此，变形网格4DDC已被证明能够预测PBS质子治疗的4D剂量分布的复杂图案，具有高剂量和几何精度，并且如果正确的时间信息可用，则其可以用作4D治疗规划、运动缓解选择和最终4D优化应用的有效临床工具。
The aim of this study was to verify the temporal accuracy of the estimated dose distribution by a 4D dose calculation (4DDC) in comparison to measurements. A single-field plan (0.6 Gy), optimised for a liver patient case (CTV volume: 403cc), was delivered to a homogeneous PMMA phantom and measured by a high resolution scintillating-CCD system at two water equivalent depths. Various motion scenarios (no motion and motions with amplitude of 10 mm and two periods: 3.7 s and 4.4 s) were simulated using a 4D Quasar phantom and logged by an optical tracking system in real-time. Three motion mitigation approaches (single delivery, 6x layered and volumetric rescanning) were applied, resulting in 10 individual measurements. 4D dose distributions were retrospectively calculated in water by taking into account the delivery log files (retrospective) containing information on the actually delivered spot positions, fluences, and time stamps. Moreover, in order to evaluate the sensitivity of the 4DDC inputs, the corresponding prospective 4DDCs were performed as a comparison, using the estimated time stamps of the spot delivery and repeated periodical motion patterns. 2D gamma analyses and dose-difference-histograms were used to quantify the agreement between measurements and calculations for all pixels with >5% of the maximum calculated dose. The results show that a mean gamma score of 99.2% with standard deviation 1.0% can be achieved for 3%/3 mm criteria and all scenarios can reach a score of more than 95%. The average area with more than 5% dose difference was 6.2%. Deviations due to input uncertainties were obvious for single scan deliveries but could be smeared out once rescanning was applied. Thus, the deforming grid 4DDC has been demonstrated to be able to predict the complex patterns of 4D dose distributions for PBS proton therapy with high dosimetric and geometric accuracy, and it can be used as a valid clinical tool for 4D treatment planning, motion mitigation selection, and eventually 4D optimisation applications if the correct temporal information is available.