Dosimetric and Treatment Delivery Analysis of Volumetric Modulated Arc Therapy systems for Pharyngeal Carcinoma

Introduction: This study evaluated the dosimetric performance and delivery efficiency of three volumetric modulated arc therapy (VMAT) techniques using different multileaf collimator (MLC) systems: MLCi2, Agility and HDMLC for the treatment of pharyngeal cancer.Material and Methods: A retrospective analysis of 21 pharyngeal cancer patients was performed. For each patient, three VMAT plans were generated using a simultaneous integrated boost (SIB) technique, delivering 66 Gy, 60 Gy and 54 Gy to PTV66, PTV60 and PTV54 respectively, over 30 fractions. Plans were created in Monaco treatment planning system (TPS) with MLCi2 (VMAT1) and Agility (VMAT2) and in Eclipse TPS with HDMLC (RapidArc). Plan quality was evaluated using conformity index (CI), homogeneity index (HI) and mean dose for target volumes. Organ-at-risk (OAR) doses were assessed according to RTOG criteria, while treatment efficiency was analyzed using monitor units (MUs) and beam-on time (BOT).Results: All techniques produced clinically acceptable plans. RapidArc demonstrated superior conformity for PTV66 and significantly improved homogeneity for PTV60 and PTV54. It also achieved reduced maximum doses to the spinal cord and decreased low- and medium-dose spillage to normal tissue compared with VMAT1 and VMAT2. RapidArc required fewer MUs and achieved shorter BOT (p < 0.05), indicating enhanced delivery efficiency.Conclusion: While all techniques met clinical requirements, RapidArc with HDMLC achieved superior conformity, better OAR sparing and improved delivery efficiency. These findings underscore the pivotal role of MLC design and configuration in optimizing VMAT plan quality and treatment performance for head and neck cancers.