Phua Jun Hao, Mok Glen Yongjie, Tan Lloyd Kuan Rui, Park Sung Yong, Lee James Cheow Lei, Tan Hong Qi
Division of Radiation Oncology, National Cancer Centre Singapore, 30 Hospital Boulevard, 168583, Singapore.
Division of Radiation Oncology, National Cancer Centre Singapore, 30 Hospital Boulevard, 168583, Singapore; Oncology Academic Clinical Programme, Duke-NUS Medical School, 8 College Road, 169857, Singapore.
Med Dosim. 2025 Jun 26. doi: 10.1016/j.meddos.2025.05.007.
Volumetric modulated arc therapy (VMAT) is the standard of care for stereotactic treatments. During a VMAT delivery, using a single collimator angle throughout a continuous arc may be suboptimal due to variations in the target's shape in the Beam Eye's view (BEV). This work proposes a VMAT optimization method which segments a single continuous arc to allow for varying collimator angle to achieve an efficient delivery and Monitor Unit (MU) utilization. Thirteen retrospective stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) patient plans with irregularly shaped targets were used in this study. The targets were mainly cavity and meningioma due to the irregular shapes. These cases were planned originally using the Eclipse treatment planning system (TPS). These plans were then replanned with rotated collimators at specific points in each VMAT arc, where the shape of the target was deemed to have changed extensively in the BEV. The start and end gantry angles of the trajectory followed the initially approved clinical plan. The resulting plans were compared with the original clinical plans using the mean aperture ratio, total plan monitor unit (MU), total beam delivery time, patient specific quality assurance (PSQA) results and the plan dosimetric metrics. These plans were delivered using Truebeam STx with HDMLCs and PSQA was measured using the Sun Nuclear SRS MapCheck with the gamma passing rate (GPR) criteria of 3%/2 mm, 2%/2 mm, 2%/1 mm, and 1%/1 mm. The replans achieved a 15.1% reduction in MUs while maintaining the target coverage. The organ-at-risk (OAR) doses showed no significant improvement when using this approach. The beam-on time for SRS plans decreased by 20% compared the clinically approved plan, while the SRT plans showed a 5% time savings. The gamma passing rate (GPR) yielded at least 99% for 2%/1 mm, and 100% for 2%/2 mm for both the clinically approved plans and the replans, respectively. There was no statistically significant difference in GPRs across all criteria and in the plan dosimetric metrics for target and normal tissues. These results show that the proposed optimization approach improves delivery efficiency in terms of both delivery time and MU reduction.
容积调强弧形放疗（VMAT）是立体定向治疗的标准治疗方式。在VMAT治疗过程中，由于射野视角（BEV）中靶区形状的变化，在整个连续弧形照射过程中使用单一准直器角度可能并非最佳选择。本研究提出了一种VMAT优化方法，该方法将单一连续弧形分割，以允许改变准直器角度，从而实现高效照射和监测单位（MU）的利用。本研究使用了13例具有不规则形状靶区的回顾性立体定向放射外科（SRS）和立体定向放射治疗（SRT）患者计划。由于形状不规则，靶区主要为空洞和脑膜瘤。这些病例最初使用Eclipse治疗计划系统（TPS）进行计划。然后在每个VMAT弧形的特定点使用旋转准直器对这些计划进行重新计划，在这些点上，靶区的形状在BEV中被认为发生了显著变化。轨迹的起始和终止机架角度遵循最初批准的临床计划。使用平均孔径比、总计划监测单位（MU）、总射束照射时间、患者特定质量保证（PSQA）结果以及计划剂量学指标，将所得计划与原始临床计划进行比较。这些计划使用带有高剂量率多叶准直器（HDMLC）的Truebeam STx进行照射，PSQA使用Sun Nuclear SRS MapCheck进行测量，伽马通过率（GPR）标准为3%/2 mm、2%/2 mm、2%/1 mm和1%/1 mm。重新计划在保持靶区覆盖的同时，MU减少了15.1%。使用该方法时，危及器官（OAR）剂量没有显著改善。与临床批准的计划相比，SRS计划的照射时间减少了20%，而SRT计划的时间节省了5%。临床批准的计划和重新计划的伽马通过率（GPR）分别在2%/1 mm时至少为99%，在2%/2 mm时为100%。在所有标准以及靶区和正常组织的计划剂量学指标方面，GPR没有统计学上的显著差异。这些结果表明，所提出的优化方法在照射时间和MU减少方面提高了照射效率。
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