Torizuka Daichi, Uto Megumi, Takehana Keiichi, Mizowaki Takashi
Department of Radiation Oncology and Image-Applied Therapy, Kyoto University Graduate School of Medicine, Kyoto 606-8507, Japan.
J Radiat Res. 2021 Oct 2. doi: 10.1093/jrr/rrab092.
In the delivery of stereotactic radiosurgery (SRS) by linear accelerator (LINAC), dynamic conformal arc therapy (DCAT) with non-coplanar beams is conventionally used. However, volumetric modulated arc therapy (VMAT) can improve target conformity, thereby decreasing the dose to organs at risk by inversed planning methods, but few studies have directly compared DCAT and VMAT with and without non-coplanar beams in patients with single brain metastasis. We therefore conducted a planning study to compare the dose distribution in DCAT, VMAT using only a coplanar arc (CoVMAT) and VMAT with non-coplanar arcs (NcVMAT) in the treatment of single brain metastasis. DCAT, CoVMAT and NcVMAT plans were created for 15 patients. The three modalities were compared in terms of target conformity, target coverage, the dose to normal brain tissue, monitor units (MUs) and beam-on time. Both conformity indices (RTOG-CI and IP-CI) as well as the D98% of the gross target volume (GTV) were significantly better in the NcVMAT plans than in the DCAT plans. Comparisons of the doses to normal brain tissue revealed that the V20Gy, V15Gy, V12Gy, V10Gy and V5Gy were significantly smaller in the NcVMAT plans than in the plans based on the other two modalities. The MUs of the DCAT and NcVMAT plans were larger than those of the CoVMAT plans, and the beam-on time was longer in the NcVMAT and CoVMAT plans than in the DCAT plans. Compared to the CoVMAT and DCAT plans, NcVMAT plans significantly improved target conformity and reduced the doses to normal brain tissue at V20Gy, V15Gy, V12Gy, V10Gy and V5Gy.
在使用直线加速器（LINAC）进行立体定向放射外科治疗（SRS）时，传统上采用非共面射束的动态适形弧形治疗（DCAT）。然而，容积调强弧形治疗（VMAT）可通过逆向计划方法提高靶区适形性，从而降低危及器官的剂量，但很少有研究直接比较单发性脑转移瘤患者使用和不使用非共面射束时DCAT和VMAT的情况。因此，我们进行了一项计划研究，比较DCAT、仅使用共面弧形的VMAT（CoVMAT）和使用非共面弧形的VMAT（NcVMAT）在治疗单发性脑转移瘤时的剂量分布。为15例患者制定了DCAT、CoVMAT和NcVMAT计划。从靶区适形性、靶区覆盖、正常脑组织剂量、监测单位（MUs）和射束开启时间方面对这三种模式进行了比较。NcVMAT计划中的适形指数（RTOG-CI和IP-CI）以及大体靶体积（GTV）的D98%均显著优于DCAT计划。对正常脑组织剂量的比较显示，NcVMAT计划中的V20Gy、V15Gy、V12Gy、V10Gy和V5Gy显著小于基于其他两种模式的计划。DCAT和NcVMAT计划的MUs大于CoVMAT计划，且NcVMAT和CoVMAT计划的射束开启时间比DCAT计划更长。与CoVMAT和DCAT计划相比，NcVMAT计划显著提高了靶区适形性，并降低了V20Gy、V15Gy、V12Gy、V10Gy和V5Gy时正常脑组织的剂量。
