Memorial Hospital, Chattanooga, TN, USA.
Department of Radiation Oncology, University of Arkansas for Medical Sciences, Little Rock, AR, USA.
J Appl Clin Med Phys. 2021 Jan;22(1):100-108. doi: 10.1002/acm2.13113. Epub 2020 Dec 7.
To investigate a planning technique that can possibly reduce low-to-intermediate dose spillage (measured by R50%, D2cm values) in lung SBRT plans.
Dose falloff outside the target was studied retrospectively in 102 SBRT VMAT plans of lung tumor. Plans having R50% and/or D2cm higher than recommended tolerances in RTOG protocols 0813 and 0915 were replanned with new optimization constraints using novel shell structures and novel constraints. Violations in the RTOG R50% value can be rectified with a dose constraint to a novel shell structure ("OptiForR50"). The construction of structure OptiForR50% and the novel optimization criteria translate the RTOG goals for R50% into direct inputs for the optimizer. Violations in the D2cm can be rectified using constraints on a 0.5 cm thick shell structure with inner surface 2cm from the PTV surface. Wilcoxon signed-rank test was used to compare differences in dose conformity, volume of hot spots, R50%, D2cm of the target in addition to the OAR doses. A two-sided P-value of 0.05 was used to assess statistical significance.
Among 102 lung SBRT plans with PTV sizes ranging from 5 to 179 cc, 32 plans with violations in R50% or D2cm were reoptimized. The mean reduction in R50% (4.68 vs 3.89) and D2cm (56.49 vs 52.51) was statistically significant both having P < 0.01. Target conformity index, volume of 105% isodose contour outside PTV, normal lung V20, and mean dose to heart and aorta were significantly lowered with P < 0.05.
The novel planning methodology using multiple shells including the novel OptiForR50 shell with precisely calculated dimensions and optimizer constraints lead to significantly lower values of R50% and D2cm and lower dose spillage in lung SBRT plans. All plans were successfully brought into the zone of no RTOG violations.
研究一种能够降低肺部 SBRT 计划中低至中等剂量外溢（以 R50%、D2cm 值衡量）的计划技术。
回顾性研究了 102 例肺部肿瘤 SBRTVMAT 计划中外靶剂量下降情况。对于 RTOG 协议 0813 和 0915 中推荐耐受量的 R50%和/或 D2cm 较高的计划，使用新的壳结构和新的约束条件进行了重新优化。通过对新壳结构（“OptiForR50”）的剂量约束，可以纠正 RTOG R50%值的违反。结构 OptiForR50%的构建和新的优化标准将 RTOG 对 R50%的目标转化为优化器的直接输入。通过对距 PTV 表面 2cm 内表面的 0.5cm 厚壳结构上的约束，可以纠正 D2cm 的违反。使用 Wilcoxon 符号秩检验比较了靶区剂量适形性、热点体积、R50%、D2cm 以及 OAR 剂量的差异。采用双侧 P 值 0.05 来评估统计学意义。
在 PTV 大小为 5 至 179cc 的 102 例肺部 SBRT 计划中，有 32 例 R50%或 D2cm 违反的计划进行了重新优化。R50%（4.68 对 3.89）和 D2cm（56.49 对 52.51）的平均降低均具有统计学意义（均 P<0.01）。靶区适形指数、PTV 外 105%等剂量轮廓的体积、正常肺 V20 以及心脏和主动脉的平均剂量均显著降低（均 P<0.05）。
使用包括新的 OptiForR50 壳在内的多个壳的新计划方法，该壳具有精确计算的尺寸和优化器约束，可显著降低肺部 SBRT 计划中 R50%和 D2cm 的值，并降低剂量外溢。所有计划均成功进入 RTOG 无违反区域。
