Shen Jiuling, Dai Zhitao, Yu Jing, Yuan Qingqing, Kang Kailian, Chen Cheng, Liu Hui, Xie Conghua, Wang Xiaoyong
Department of Radiation and Medical Oncology, Zhongnan Hospital of Wuhan University, Wuhan, China.
Hubei Radiotherapy Quality Control Center, Wuhan University, Wuhan, China.
Front Oncol. 2022 Sep 6;12:987971. doi: 10.3389/fonc.2022.987971. eCollection 2022.
The aim of this study was to investigate the impact of collimator angle optimization in single-isocenter coplanar volume modulated arc therapy (VMAT) stereotactic radiosurgery (SRS) for multiple metastases with respect to dosimetric quality and treatment delivery efficiency. In particular, this is achieved by a novel algorithm of sub-arc collimator angle optimization (SACAO).
Twenty patients with multiple brain metastases were retrospectively included in this study. A multi-leaf collimator (MLC) conformity index (MCI) that is defined as the ratio of the area of target projection in the beam's eye view (BEV) to the related area fitted by MLC was applied. Accordingly, for each control point, 180 MCI values were calculated with a collimator angle interval of 1°. A two-dimensional heatmap of MCI as a function of control point and collimator angle for each full arc was generated. The optimal segmentation of sub-arcs was achieved by avoiding the worst MCI at each control point. Then, the optimal collimator angle for each sub-arc would be determined by maximizing the summation of MCI. Each patient was scheduled to undergo single-center coplanar VMAT SRS based on either the novel SACAO algorithm or the conventional VMAT with static collimator angle (ST-VMAT). The dosimetric parameters, field sizes, and the monitoring units (Mus) were evaluated.
The mean dose-volumetric parameters for the target volume of SACAO were comparable to ST-VMAT, while the conformity index (CI), homogeneity index (HI), and gradient index (GI) were reduced by SACAO. Improved sparing of organs at risk (OARs) was also obtained by SACAO. In particular, the SACAO method significantly ( < 0.01) reduced the field size (76.59 ± 32.55 vs. 131.95 ± 56.71 cm) and MUs (655.35 ± 71.99 vs. 729.85 ± 73.52) by 41.11%.
The SACAO method could be superior in improving the CI, HI, and GI of the targets as well as normal tissue sparing for multiple brain metastases SRS. In particular, SACAO has the potential of increasing treatment efficiency in terms of field size and MU.
本研究旨在探讨在单等中心共面容积调强弧形放疗（VMAT）立体定向放射外科治疗（SRS）中，准直器角度优化对多发转移瘤的剂量学质量和治疗实施效率的影响。具体而言，这是通过一种新的子弧形准直器角度优化（SACAO）算法实现的。
本研究回顾性纳入了20例多发脑转移瘤患者。应用多叶准直器（MLC）适形指数（MCI），其定义为射野方向观（BEV）中靶区投影面积与MLC拟合的相关面积之比。因此，对于每个控制点，以1°的准直器角度间隔计算180个MCI值。生成每个完整弧形的MCI作为控制点和准直器角度函数的二维热图。通过避免每个控制点处最差的MCI来实现子弧形的最佳分割。然后，通过最大化MCI的总和来确定每个子弧形的最佳准直器角度。每位患者计划根据新的SACAO算法或传统的静态准直器角度VMAT（ST-VMAT）进行单中心共面VMAT SRS。评估剂量学参数、射野大小和监测单位（MU）。
SACAO靶区体积的平均剂量体积参数与ST-VMAT相当，而SACAO降低了适形指数（CI）、均匀性指数（HI）和梯度指数（GI）。SACAO还改善了危及器官（OAR）的保护。特别是，SACAO方法显著（<0.01）减小了射野大小（76.59±32.55 vs.131.95±56.71 cm）和MU（655.35±71.99 vs.729.85±73.52），降幅达41.11%。
SACAO方法在改善多发脑转移瘤SRS的靶区CI、HI和GI以及保护正常组织方面可能更具优势。特别是，SACAO在射野大小和MU方面具有提高治疗效率的潜力。
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