Oshiro Yoshiko, Kato Yuichi, Mizumoto Masashi, Sakurai Hideyuki
Radiation Oncology, Tsukuba Medical Center Hospital, Tsukuba, JPN.
Radiation Oncology, University of Tsukuba Hospital, Tsukuba, JPN.
Cureus. 2024 Apr 23;16(4):e58816. doi: 10.7759/cureus.58816. eCollection 2024 Apr.
To compare the plan quality of stereotactic radiosurgery (SRS) between 2.5-mm and 5-mm multileaf collimator (MLC) and investigate the factors' influence on the differences by MLC size.
Seventy-six treatment plans including 145 targets calculated with a single isocenter multiple noncoplanar dynamic conformal arc (DCA) technique using automatic multiple brain metastases (MBM) treatment planning system. Conformity index (CI), gradient index (GI), lesion underdosage volume factor (LUF), healthy tissue overdose volume factor (HTOF), geometric conformity index (g), and mean dose to normal organs were compared between 2.5-mm and 5-mm MLC. Then the factors that influenced the differences of these parameters were investigated. The impact of target size was also investigated for CI and GI values of individual targets (n=145), and differences between 2.5-mm and 5-mm MLC were analyzed.
All parameters except for LUF were significantly better in plans with 2.5 mm MLC. Target size was a significant factor for difference in HTOF, and distance between targets was a significant factor for difference in brain dose and GI. Among 145 metastases, the average inverse CI was 1.35 and 1.47 with 2.5-mm and 5-mm MLC, respectively (p<0.001). The average GI was 3.21 and 3.53, respectively (p<0.001). For individual targets, target size was a significant factor in CI and GI both with 2.5-mm and 5-mm MLC (p-value: <0.001, each). CI and GI were significantly better with 2.5-mm than 5-mm MLC. CI was almost >0.67 except for ≤5mm targets with 5-mm MLC. Also, GI was almost smaller than 3.0 for >10 mm targets both with 2.5-mm and 5-mm MLC.
MBM with 5-mm MLC was almost fine. However, it may be better to use a conservative margin for larger metastases. It may also be better to avoid SRS with 5-mm MLC for patients with ≤5 mm target size.
比较2.5毫米和5毫米多叶准直器（MLC）在立体定向放射外科手术（SRS）中的计划质量，并研究MLC尺寸对差异的影响因素。
使用自动多发性脑转移瘤（MBM）治疗计划系统，采用单等中心多非共面动态适形弧（DCA）技术计算76个治疗计划，包括145个靶区。比较2.5毫米和5毫米MLC之间的适形指数（CI）、梯度指数（GI）、靶区低剂量体积因子（LUF）、健康组织高剂量体积因子（HTOF）、几何适形指数（g）以及正常器官的平均剂量。然后研究影响这些参数差异的因素。还研究了靶区大小对单个靶区（n = 145）的CI和GI值的影响，并分析了2.5毫米和5毫米MLC之间的差异。
除LUF外，所有参数在2.5毫米MLC的计划中均显著更好。靶区大小是HTOF差异的显著因素，靶区之间的距离是脑剂量和GI差异的显著因素。在145个转移瘤中，2.5毫米和5毫米MLC的平均反向CI分别为1.35和1.47（p < 0.001）。平均GI分别为3.21和3.53（p < 0.001）。对于单个靶区，靶区大小在2.5毫米和5毫米MLC的CI和GI中均为显著因素（p值均< 0.001）。2.5毫米MLC的CI和GI显著优于5毫米MLC。除5毫米MLC的≤5毫米靶区外，CI几乎> 0.67。同样，对于2.5毫米和5毫米MLC的> 10毫米靶区，GI几乎均小于3.0。
5毫米MLC的MBM基本良好。然而，对于较大的转移瘤，使用保守边界可能更好。对于靶区大小≤5毫米的患者，避免使用5毫米MLC进行SRS可能也更好。
