Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, 100021, China.
Radiat Oncol. 2022 May 7;17(1):86. doi: 10.1186/s13014-022-02059-6.
This study implemented a piecewise volumetric modulated arc therapy (P-VMAT) for realizing whole-brain radiation therapy (WBRT) with simultaneous integrated boost (SIB) for multiple brain metastases (> 40 metastases) with a conventional C-arm linear accelerator.
This study retrospectively analyzed 10 patients with multiple brain metastases (40-120 metastases, median 76), who underwent WBRT and SIB using helical tomotherapy (HT). The prescribed doses were 40 Gy/20 f and 60 Gy/20 f for WBRT and SIB, respectively. Corresponding new HT plans were designed with P-VMAT using 7 arcs. For each arc, the collimator was rotated to 45°, and the field width was limited to 2.5 cm with 0.5 cm overlap with adjacent arcs. Thus, each arc covered only one section of the brain target volume. A conventional dual arc VMAT (DA-VMAT) plan was also designed. HT, P-VMAT, and DA-VMAT plans were compared using dose distribution reviews and dosimetric parameters. ArcCHECK phantom measurements were performed for verification of P-VMAT plans.
No significant differences in the mean coverage of the whole-brain target and metastases were observed between HT and P-VMAT (p > 0.05). The conformity index for the whole-brain target improved with P-VMAT compared with HT (p < 0.05). Furthermore, the volume of 44 Gy V (110% of prescribed dose for WBRT) received for whole-brain significantly reduced with P-VMAT from 38.2 ± 12.9% to 23.3 ± 9.4% (p < 0.05), and the maximum dose for organs at risks such as the hippocampus, optical nerve, optical chiasm, and spinal cord declined with P-VMAT (p < 0.05). Unlike HT and P-VMAT, DA-VMAT was clinically unacceptable because V in the whole-brain was too high (54.7 ± 8.2%). The mean absolute dose gamma passing rate for P-VMAT plans was 97.6 ± 1.1% (3%/3 mm criterion, 10%).
P-VMAT is favorable for WBRT and SIB for multiple brain metastases. It provides comparable coverage of whole-brain target and SIB, with better conformity, lower V and better dose sparing of organs at risk compared with HT. Furthermore, results show that DA-VMAT fails clinical practice even for a relatively large number of brain metastases with a high degree of plan complexity. The patient specific verification demonstrates the feasibility of P-VMAT for clinical application.
本研究使用常规 C 臂直线加速器为多个脑转移瘤（>40 个转移瘤，中位数 76 个）实施分段容积调强弧形治疗（P-VMAT），以实现全脑放疗（WBRT）同步推量（SIB）。
本研究回顾性分析了 10 例接受螺旋断层放疗（HT）治疗的多发性脑转移瘤（40-120 个转移瘤，中位数 76 个）患者。WBRT 和 SIB 的处方剂量分别为 40 Gy/20 f 和 60 Gy/20 f。采用 7 个弧设计相应的新 HT 计划。对于每个弧，准直器旋转 45°，射野宽度限制为 2.5cm，与相邻弧重叠 0.5cm。因此，每个弧仅覆盖脑靶区的一个部分。还设计了常规双弧调强弧形治疗（DA-VMAT）计划。通过剂量分布评价和剂量学参数比较 HT、P-VMAT 和 DA-VMAT 计划。进行弧形核查模体测量以验证 P-VMAT 计划。
HT 和 P-VMAT 之间全脑靶区和转移瘤的平均覆盖率无显著差异（p>0.05）。与 HT 相比，P-VMAT 使全脑靶区的适形指数提高（p<0.05）。此外，P-VMAT 使全脑接受 44 Gy V（WBRT 处方剂量的 110%）的体积从 38.2±12.9%显著减少至 23.3±9.4%（p<0.05），并且海马体、视神经、视交叉和脊髓等危及器官的最大剂量降低（p<0.05）。与 HT 和 P-VMAT 不同，DA-VMAT 由于全脑 V 过高（54.7±8.2%）而在临床上不可接受。P-VMAT 计划的平均绝对剂量伽马通过率为 97.6±1.1%（3%/3mm 标准，10%）。
P-VMAT 有利于多个脑转移瘤的 WBRT 和 SIB。与 HT 相比，它提供了相当的全脑靶区覆盖率和 SIB，更好的适形性，更低的 V 和更好的危及器官剂量保护。此外，结果表明，即使对于具有高度计划复杂性的相对大量脑转移瘤，DA-VMAT 也无法在临床上实施。患者特定的验证表明 P-VMAT 具有临床应用的可行性。
