Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, 63110, USA.
Department of Radiation Oncology, Yonsei Cancer Center, Yonsei University College of Medicine, Seoul, South Korea.
Radiat Oncol. 2018 Mar 24;13(1):51. doi: 10.1186/s13014-018-1000-7.
To simplify the adaptive treatment planning workflow while achieving the optimal tumor-dose coverage in pancreatic cancer patients undergoing daily adaptive magnetic resonance image guided radiation therapy (MR-IGRT).
In daily adaptive MR-IGRT, the plan objective function constructed during simulation is used for plan re-optimization throughout the course of treatment. In this study, we have constructed the initial objective functions using two methods for 16 pancreatic cancer patients treated with the ViewRay™ MR-IGRT system: 1) the conventional method that handles the stomach, duodenum, small bowel, and large bowel as separate organs at risk (OARs) and 2) the OAR grouping method. Using OAR grouping, a combined OAR structure that encompasses the portions of these four primary OARs within 3 cm of the planning target volume (PTV) is created. OAR grouping simulation plans were optimized such that the target coverage was comparable to the clinical simulation plan constructed in the conventional manner. In both cases, the initial objective function was then applied to each successive treatment fraction and the plan was re-optimized based on the patient's daily anatomy. OAR grouping plans were compared to conventional plans at each fraction in terms of coverage of the PTV and the optimized PTV (PTV OPT), which is the result of the subtraction of overlapping OAR volumes with an additional margin from the PTV.
Plan performance was enhanced across a majority of fractions using OAR grouping. The percentage of the volume of the PTV covered by 95% of the prescribed dose (D) was improved by an average of 3.87 ± 4.29% while D coverage of the PTV OPT increased by 3.98 ± 4.97%. Finally, D coverage of the PTV demonstrated an average increase of 6.47 ± 7.16% and a maximum improvement of 20.19%.
In this study, our proposed OAR grouping plans generally outperformed conventional plans, especially when the conventional simulation plan favored or disregarded an OAR through the assignment of distinct weighting parameters relative to the other critical structures. OAR grouping simplifies the MR-IGRT adaptive treatment planning workflow at simulation while demonstrating improved coverage compared to delivered pancreatic cancer treatment plans in daily adaptive radiation therapy.
为简化自适应治疗计划流程，同时实现胰腺癌患者每日自适应磁共振图像引导放疗（MR-IGRT）的最佳肿瘤剂量覆盖，我们提出了一种新的方法。
在每日自适应 MR-IGRT 中，在整个治疗过程中，使用模拟过程中构建的计划目标函数对计划进行重新优化。在这项研究中，我们使用两种方法为 16 名接受 ViewRay™ MR-IGRT 系统治疗的胰腺癌患者构建了初始目标函数：1）常规方法，将胃、十二指肠、小肠和大肠分别作为危及器官（OAR）处理；2）OAR 分组方法。使用 OAR 分组，创建一个包含这些四个主要 OAR 中位于计划靶区（PTV）3cm 内部分的组合 OAR 结构。对 OAR 分组模拟计划进行优化，使靶区覆盖范围与常规方法构建的临床模拟计划相当。在这两种情况下，然后将初始目标函数应用于每个连续的治疗分次，并根据患者的每日解剖结构重新优化计划。在每个分次中，将 OAR 分组计划与常规计划进行比较，比较指标包括 PTV 和优化的 PTV（PTV OPT）的覆盖情况，PTV OPT 是从 PTV 中减去重叠 OAR 体积并额外增加一个边界得到的结果。
使用 OAR 分组可以提高大多数分次的计划性能。95%的处方剂量（D）覆盖 PTV 的体积百分比平均提高了 3.87%±4.29%，而 PTV OPT 的 D 覆盖范围增加了 3.98%±4.97%。最后，PTV 的 D 覆盖范围平均增加了 6.47%±7.16%，最大改善幅度为 20.19%。
在这项研究中，我们提出的 OAR 分组计划总体上优于常规计划，尤其是在常规模拟计划通过为其他关键结构分配不同的权重参数来偏向或忽视 OAR 时。OAR 分组简化了 MR-IGRT 自适应治疗计划流程，在模拟阶段简化了工作流程，同时与每日自适应放疗中实际的胰腺癌治疗计划相比，提高了覆盖范围。
