Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Canada.
Department of Radiation Oncology, Dalhousie University, Halifax, Canada.
J Appl Clin Med Phys. 2024 Sep;25(9):e14396. doi: 10.1002/acm2.14396. Epub 2024 Jun 18.
Noncoplanar arc optimization has been shown to reduce OAR doses in SRS/SRT and has the potential to reduce doses to OARs in SBRT. Extracranial targets have additional considerations, including large OARs and, in the case of the liver, volume constraints on the healthy liver. Considering pathlengths through OARs that encompass target volumes may lead to specific dose reductions as in the encompassing healthy liver tissue. These optimizations must also leverage delivery efficiency and trajectory sampling to ensure ease of clinical translation. The purpose of this research is to generate optimized static-couch arcs that separately consider serial and parallel OARs and arc delivery efficiency, with a trajectory sampling metric, towards the aim of reducing dose to OARs and the surrounding healthy liver tissue. Separate BEV cost maps were created for parallel, and serial OARs by means of a fast ray-triangle intersection algorithm. An additional BEV cost map was created for the liver which, by definition, encompasses the liver tumors. The individual costs of these maps were summed and combined with the sampling metric for 100 000 random combinations of arc trajectories. A search algorithm was applied to find an arc trajectory solution that satisfied BEV cost and sampling optimization, while also ensuring an efficient delivery was possible with a low number of arcs. This method of arc selection was evaluated for 16 liver SBRT patients characterized by small and large target volumes. Comparisons were made with a clinical arc template of coplanar arcs. Dosimetric plan quality was evaluated using published guidelines and metrics from RTOG1112. Four of five plan quality metrics for the liver were significantly reduced when planned with optimized noncoplanar arcs. Median (range) reductions of the volumes receiving 10, 18, and 21 Gy were found of 140.4 (295.8) cc (p = 0.001), 28.2 (230.6) cc (p = 0.002) and 18.5 (155.5) cc (p = 0.04). A significant increase in median (range) dose to the right kidney of 0.2 ± 0.9 Gy (p = 0.03) was also found using optimized noncoplanar arcs, which was below the tolerance of 10 Gy for all cases. The average number of arcs chosen was 4 ± 1. Optimizing serial and parallel OARs separately during static couch noncoplanar arc selection significantly reduced the dose to the liver during SBRT using a moderate number of arcs.
非共面弧优化已被证明可以降低 SRS/SRT 中的 OAR 剂量，并且有可能降低 SBRT 中 OAR 的剂量。颅外靶区有其他需要考虑的因素，包括大的 OAR，以及在肝脏的情况下，健康肝脏的体积限制。考虑到通过包含靶区的 OAR 的路径长度可能会导致特定的剂量降低，就像包含健康的肝组织一样。这些优化还必须利用输送效率和轨迹采样来确保易于临床转化。本研究的目的是生成分别考虑串行和并行 OAR 以及弧形输送效率的优化静态躺椅弧形，使用轨迹采样指标，以达到降低 OAR 剂量和周围健康肝组织剂量的目的。通过快速射线-三角形交叉算法为并行和串行 OAR 分别创建了单独的 BEV 成本图。为肝脏创建了另一个 BEV 成本图，根据定义，该图包含肝脏肿瘤。这些地图的个别成本相加，并与 100000 个弧形轨迹的采样指标相结合。应用搜索算法来找到满足 BEV 成本和采样优化的弧形轨迹解决方案，同时还确保可以通过少量弧形实现高效输送。这种弧形选择方法评估了 16 例肝脏 SBRT 患者，这些患者的靶区体积较小或较大。与共面弧形的临床弧形模板进行了比较。使用 RTOG1112 发布的指南和指标评估了剂量学计划质量。当使用优化的非共面弧形进行计划时，肝脏的五个计划质量指标中有四个显著降低。发现接受 10、18 和 21 Gy 的体积中位数（范围）减少了 140.4（295.8）cc（p=0.001）、28.2（230.6）cc（p=0.002）和 18.5（155.5）cc（p=0.04）。还发现使用优化的非共面弧形时，右肾的中位（范围）剂量显著增加了 0.2±0.9 Gy（p=0.03），所有病例均低于 10 Gy 的耐受剂量。选择的弧形数量平均为 4±1。在静态躺椅非共面弧形选择过程中分别优化串行和并行 OAR 可显著降低 SBRT 中肝脏的剂量，同时使用数量适中的弧形。
