多发脑转移瘤VMAT计划中MLC插指功能剂量学研究

目的 通过比较有无MLC插指功能的VMAT计划剂量学差异,探究MLC插指在多发脑转移瘤VMAT计划中的优势。方法 回顾本院 15例多发脑转移瘤患者数据。首先在定位CT图像上设计有MLC插指功能权限的双弧VMAT计划(VMAT-1)。随后不改变计划参数,摒弃插指功能权限,重新优化计算得到无MLC插指功能的VMAT-2计划。比较两种计划在靶区CI和HI、OAR受量、机器跳数、控制点数、计划执行时间和计划耗时方面差异。采用Wilcoxon符号秩和检验。结果 VMAT-1的均匀性优于VMAT-2(P=0.04),两种计划的适形度基本相当(P=0.33)。VMAT-1计划中PTV的 D_98%高于VMAT-2(P=0.04)。VMAT-1中的脑干 D_mean比VMAT-2降低了4%(P=0.04),其他OAR参数基本相当。部分病例显示VMAT-1计划有着相邻横断面的肿瘤交界处正常组织受量更少的特点。VMAT-1计划机器跳数比VMAT-2增加了4%(P=0.01)。两种计划的控制点数和预估执行时间相近(P=0.81、0.73)。VMAT-1的计划制作耗时较VMAT-2减少了26%(P=0.00)。结论 在多发脑转移瘤VMAT计划中,MLC插指功能可缩短VMAT优化时间,提高优化效率。

A dosimetric study of multileaf collimator interdigitation in volumetric modulated arc therapy plans for multiple brain metastases

Objective To evaluate the dosimetric difference between volumetric modulated arc therapy (VMAT) plans with and without an interdigitating multileaf collimator (MLC) in the treatment of multiple brain metastases, and to investigate the advantages of MLC interdigitation in VMAT plans for multiple brain metastasis. Methods A retrospective study was performed on clinical data from 15 patients with multiple brain metastases in our hospital. A dual arc VMAT plan with an interdigitating MLC ( VMAT-1) was designed on computed tomography ( CT) images. Then, keeping all parameters unchanged, another VMAT plan with a non-interdigitating MLC ( VMAT-2) was made after re-optimization. The conformity index ( CI) and homogeneity index ( HI) of the planning target volume ( PTV) , doses to organs at risk ( OARs) , monitor units (MUs), control points, delivery time, and planning time were compared between the two treatment plans using the Wilcoxon signed rank test. Results VMAT-1 achieved a better HI than VMAT-2 ( P=0. 04) , while there was no significant difference in CI between the two plans ( P=0. 33) . VMAT-1 had a significantly higher D98% for PTV than VMAT-2(P=0. 04). Compared with VMAT-2, the Dmean to the brain stem in VMAT-1 was significantly reduced by 4%(P=0. 04). The doses to other OARs in VMAT-1 were similar to those in VMAT-2. In some patients, compared with VMAT-2, VMAT-1 had a lower dose to normal tissue at the junction of neighboring CT planes of tumor. Compared with VMAT-2, the MUs of VMAT-1 were significantly increased by 4%( P=0. 01 ) , while there were no significant differences in control points or delivery time between the two plans (P=0. 81, 0. 73). VMAT-1 had the planning time significantly reduced by 26% compared with VMAT-2 ( P= 0. 00 ) . Conclusions In VMAT plans for multiple brain metastases, MLC interdigitation could save the VMAT planning time and improve the planning efficiency.