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: MLCi۲, Agility and HDMLC for the treatment of pharyngeal cancer. Material and Methods: A retrospective analysis of ۲۱ pharyngeal cancer patients was performed. For each patient, three VMAT plans were generated using a simultaneous integrated boost (SIB) technique, delivering ۶۶ Gy, ۶۰ Gy and ۵۴ Gy to PTV۶۶, PTV۶۰ and PTV۵۴ respectively, over ۳۰ fractions. Plans were created in Monaco treatment planning system (TPS) with MLCi۲ (VMAT۱) and Agility (VMAT۲) 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 PTV۶۶ and significantly improved homogeneity for PTV۶۰ and PTV۵۴. It also achieved reduced maximum doses to the spinal cord and decreased low- and medium-dose spillage to normal tissue compared with VMAT۱ and VMAT۲. RapidArc required fewer MUs and achieved shorter BOT (p < ۰.۰۵), 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.

کلیدواژه ها:

Pharyngeal neoplasms ، Radiotherapy planning ، Multileaf Collimator ، volumetric modulated arc therapy ، Organs At Risk