Chen Jiayun, Cui Weijie, Fu Qi, Zhang Haojia, Huang Xiaodong, Han Fei, Xia Wenlong, Liang Bin, Dai Jianrong
National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China.
Department of Oncology, The Affiliated Hospital of Guizhou Medical University, Guiyang, China.
J Appl Clin Med Phys. 2020 Nov;21(11):37-47. doi: 10.1002/acm2.13020. Epub 2020 Oct 12.
Maximum leaf speed is a configurable parameter of MLC in a treatment-planning system. This study investigated the influence of MLC on the quality of VMAT plans.
Seven MLCs with different maximum leaf speeds (1.0, 1.5, 2.25, 3.5, 5.0, 7.5, and 10 cm/s) were configured for an accelerator in treatment-planning system. Correspondingly, seven treatment plans, with the identical initial optimization parameter, were designed with the mdaccAutoPlan system. Six nasopharyngeal carcinoma (NPC) patients and nine rectal cancer patients were selected, representing complex and simple clinical circumstances. VMAT plan quality was evaluated with PlanIQ software. The results were statistically analyzed with a one-way analysis of variance (ANOVA) and pairwise comparison tests.
The relative changes of plan scores achieved by the seven configured accelerators, with specific maximum MLC leaf speed (MMLS) for each patient, were studied. Two apparent trends of MMLS influence on VMAT plan scores were observed: Plan scores increased with MMLS; Plan scores increased rapidly when MMLS increased from 1 to 3.5, thus the relative change of plan score decreased in this MMLS range. The stationary point of maximum MLC speed (MMSSP) is defined, for the specific MMLS when the relative changes of plan scores is first <5%, as MMLS increases from 1.0 to 10. For rectal plans, MMSSPs were 2.25 for six patients and 3.5 for the other three patients. For NPC plans, MMSSPs were 3.5 for five patients and 2.25 for one patient.
This work indicates that MMLS directly influences VMAT plan quality in NPC cases and rectal cancer cases. VMAT plan quality improved conspicuously as MMLS increased from 1 to 3.5, VMAT plan quality with marginal improvement when MMLS is above 3.5.
最大叶片速度是治疗计划系统中多叶准直器（MLC）的一个可配置参数。本研究调查了MLC对容积调强弧形治疗（VMAT）计划质量的影响。
在治疗计划系统中为一台加速器配置了七种具有不同最大叶片速度（1.0、1.5、2.25、3.5、5.0、7.5和10厘米/秒）的MLC。相应地，使用mdaccAutoPlan系统设计了七个具有相同初始优化参数的治疗计划。选取了六例鼻咽癌（NPC）患者和九例直肠癌患者，分别代表复杂和简单的临床情况。使用PlanIQ软件评估VMAT计划质量。结果采用单因素方差分析（ANOVA）和两两比较检验进行统计学分析。
研究了七种配置加速器在每个患者特定的最大MLC叶片速度（MMLS）下所获得的计划分数的相对变化。观察到MMLS对VMAT计划分数影响的两个明显趋势：计划分数随MMLS增加而增加；当MMLS从1增加到3.5时，计划分数迅速增加，因此在该MMLS范围内计划分数的相对变化减小。将最大MLC速度的固定点（MMSSP）定义为，当MMLS从1.0增加到10时，计划分数的相对变化首次<5%时的特定MMLS。对于直肠癌计划，六例患者的MMSSP为2.25，另外三例患者为3.5。对于NPC计划，五例患者的MMSSP为3.5，一例患者为2.25。
本研究表明，MMLS直接影响NPC病例和直肠癌病例的VMAT计划质量。当MMLS从1增加到3.5时，VMAT计划质量显著提高，当MMLS高于3.5时，VMAT计划质量有边际改善。
