Abstract
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°. Key words: Esophageal neoplasms/volumetric modulated arc therapy; Collimator angle; Max delivery time; Gantry spacing
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