颈上段食管癌VMAT计划设计参数的研究

A study of parameters of a volumetric modulated arc therapy plan for cervical and upper esophageal cancer

目的：评估不同计划设计参数条件下颈、上段食管癌VMAT计划质量，得出最优计划设计参数值，以期为临床VMAT治疗计划设计提供参考。方法选择颈、上段食管癌患者各10例，使用核通 Oncentra 4.3 TPS，医科达Synergy VMAT直线加速器。采用机架步进角度2°、3°、4°，最大出束时间80、110、150 s，准直器角度0°、45°制定6套VMAT计划。统计PTV和OAR受量，配对t检验差异。结果颈段食管癌准直器角度45°的VMAT计划质量优于0°（P＝0．003～0.007）。颈段食管癌最大出束时间110、150 s的VMAT计划质量与80 s相近（ P＞0.05），80 s VMAT计划PTV的D90、V105优于110 s计划组（ P＝0.011、0.010），PTV D100优于150 s组（ P＝0.004）；110 s组的D98优于80 s组（ P＝0.034）；靶区的其他参数及OAR比较均无统计学差异（ P＞0.05）；上段食管癌3个最大出束时间的VMAT计划质量均相近（ P＞0.05）。颈段食管癌机架步进角度3°的VMAT计划质量优于2°、4°（ P＝0．010～0.048）；上段食管癌机架步进角度3°的 VMAT 计划 PTVmean、CORD D2优于4°计划（ P＝0.014、0.005），与2°比较靶区剂量分布PTV D100略好（P＝0.046），但肺组织V25、V30受量略高（P＝0.007、0.026）。结论对于颈、上段食管癌VMAT计划，45°准直器角度、80 s最大出束时间、3°机架步进角度为VMAT计划最优的设计参数初始值。

Objective To figure out the optimal parameters of a volumetric modulated arc therapy （ VMAT） plan for cervical and upper esophageal cancer by quality evaluation of VMAT plans with different parameters, and to provide a reference for the design of clinical VMAT treatment plan. Methods Ten patients with cervical esophageal cancer and ten patients with upper esophageal cancer were enrolled as subjects. The Nucletron Oncentra 4. 3 treatment planning system was used to generate plans for Elekta Synergy VMAT accelerator. Six VMAT plans were made with variation in the gantry angle （ 2°, 3°, and 4°）, the maximum delivery time （80 s, 110 s, and 150 s）, and the collimator angle （0° and 45°）. The doses to the planning target volume and organs at risk were analyzed by paired t test. Results For cervical and upper esophageal cancer, the quality of VMAT plans with a collimator angle of 45° was better than those with a collimator angle of 0°（P=0. 003-0. 007）. For cervical esophageal cancer, there was no significant difference in quality between VMAT plans with a maximum delivery time of 110 s or 150 s and those with a maximum delivery time of 80 s （ P〉0. 05 ）;for upper esophageal cancer, there was also no significant difference in quality between VMAT plans with three different maximum delivery times （ P〉0. 05 ） . For cervical esophageal cancer, the VMAT plans with a gantry angle of 3° had a better quality than those with a gantry angle of 2° or 4°（P=0. 010-0. 048）. For upper esophageal cancer, the VMAT plans with a gantry angle of 3° had a better quality than those with a gantry angle of 4° （ P=0. 010-0. 048） . Compared with those with a gantry angle of 2° , the VMAT plans with a gantry angle of 3° had a slightly better dose distribution in the target volume （ P=0. 046 ） , but a slightly higher dose to lung tissue （ V25 and V30 , P=0. 007 and 0. 026） . Conclusions The optimal initial parameters of a VMAT plan for cervical and upper esophageal cancer are a collimator angle of 45°, a maximum delivery time of 80 s, and a gantry angle of 3°.