Chiang Pin-Yi, Hung Chao-Hsiung, Chang Chih-Chia, Lee Cheng-Yen, Wang Yu-Wen, Tsang Yuk-Wah
Department of Radiation Oncology, Ditmanson Medical Foundation Chia-Yi Christian Hospital, Chiayi City, Taiwan (R.O.C.).
Department of Radiation Oncology, Chiayi Chang Gung Memorial Hospital, Chiayi County, Taiwan (R.O.C.).
Med Dosim. 2023;48(3):134-139. doi: 10.1016/j.meddos.2023.02.002. Epub 2023 Apr 2.
Whole-brain radiotherapy (WBRT) can alleviate symptoms in patients with brain metastases. However, WBRT may damage the hippocampus. Volumetric modulated arc therapy (VMAT) can achieve a suitable coverage of the target region and a more conforming dose distribution whereas decreasing the dose to organs-at-risk (OARs). Herein, we aimed to compare the differences between treatment plans utilizing coplanar VMAT and noncoplanar VMAT in hippocampal-sparing WBRT (HS-WBRT). Ten patients were included in this study. For each patient, the Eclipse A10 treatment planning system was used to generate 1 coplanar VMAT (C-VMAT) and 2 noncoplanar VMAT treatment plans with various beam angles (noncoplanar VMAT A [NC-A] and noncoplanar VMAT B [NC-B]) for HS-WBRT. The prescribed dose was 30 Gy in 12 fractions. Treatment plans were established based on the OAR dose constraints of the Radiation Therapy Oncology Group 0933 (RTOG 0933). Parameters such as the global maximum dose, dose conformity, dose homogeneity of plans, and OAR doses were evaluated. The maximum biologically equivalent doses in 2-Gy fractions (EQD2) of OARs in C-VMAT were 9.17 ± 0.61, 42.79 ± 2.00, and 42.84 ± 3.52 Gy in the hippocampus, brain stem, and optic chiasm, respectively, which were the lowest among the 3 treatment plans. There was no significant difference in dose conformity among the 3 treatment plans. However, NC-A had a slightly better conformity than C-VMAT and NC-B. NC-A had the best homogeneity, and NC-B had the worst homogeneity (p = 0.042). NC-A and NC-B had the lowest and highest global dose maximum, respectively. Therefore, NC-A, which had an intermediate performance in terms of OAR doses, had the best quality parameters. We used the quality score table based on the p-value to evaluate the significant difference between each treatment technique from the multiparameter results. In terms of treatment plan parameters, only NC-A received a score of 2; for OAR doses, C-VMAT, NC-A, and NC-B received a score of 6, 3, and 5, respectively. For the overall evaluation, C-VMAT, NC-A, and NC-B received a total score of 6, 5, and 5, respectively. Rather than noncoplanar VMAT, 3 full-arc C-VMATs should be utilized in HS-WBRT. C-VMAT can simultaneously maintain treatment plan quality and decrease patient alignment time and total treatment time.
全脑放疗（WBRT）可缓解脑转移患者的症状。然而，WBRT可能会损伤海马体。容积调强弧形放疗（VMAT）能够实现对靶区的合适覆盖以及更符合要求的剂量分布，同时降低危及器官（OARs）的剂量。在此，我们旨在比较在海马体保护全脑放疗（HS-WBRT）中使用共面VMAT和非共面VMAT的治疗计划之间的差异。本研究纳入了10例患者。对于每位患者，使用Eclipse A10治疗计划系统生成1个共面VMAT（C-VMAT）和2个用于HS-WBRT的具有不同射野角度的非共面VMAT治疗计划（非共面VMAT A [NC-A]和非共面VMAT B [NC-B]）。处方剂量为30 Gy，分12次给予。根据放射肿瘤学组0933（RTOG 0933）的OAR剂量限制制定治疗计划。评估了诸如全局最大剂量、剂量适形度、计划的剂量均匀性以及OAR剂量等参数。C-VMAT中OARs的2-Gy分次最大生物等效剂量（EQD2）在海马体、脑干和视交叉中分别为9.17±0.61、42.79±2.00和42.84±3.52 Gy，是3种治疗计划中最低的。3种治疗计划在剂量适形度方面无显著差异。然而，NC-A的适形度略优于C-VMAT和NC-B。NC-A的均匀性最佳，NC-B的均匀性最差（p = 0.042）。NC-A和NC-B的全局剂量最大值分别最低和最高。因此，在OAR剂量方面表现中等的NC-A具有最佳的质量参数。我们使用基于p值的质量评分表从多参数结果评估每种治疗技术之间的显著差异。就治疗计划参数而言，只有NC-A得分为2；对于OAR剂量，C-VMAT、NC-A和NC-B分别得分为6、3和5。对于总体评估，C-VMAT、NC-A和NC-B的总分分别为6、5和5。在HS-WBRT中应使用3个全弧C-VMAT而非非共面VMAT。C-VMAT可同时维持治疗计划质量并减少患者摆位时间和总治疗时间。
