Assessment of collimator angle variation in volumetric-modulated arc therapy planning for head and neck carcinoma patients

Abstract

Background & Aims: The collimator angle significantly impacts radiation leakage between the multi-leaf collimator (MLCs) leaves. This study aims to examine dose-volume evaluation in planning target volume (PTV) and organs at risk (OARs) for Head & Neck patients undergoing volumetric-modulated arc therapy (VMAT) with 2.5 arcs and varying collimator angles. Materials & Methods: In this experimental study, five patients with nasopharyngeal cancer were selected for treatment with the VMAT method. CT images were prepared using a CT simulator and transferred to the treatment planning system. For optimizing VMAT plans, volume and dose constraints were applied to OARs and PTVs by the algorithm. Then, the doses were calculated using the AAA algorithm. Results: Although no significant differences were observed in DVH curves across different collimator angles, other parameters exhibited variations. Notably, in Head & Neck cancer patients, optimal values for dose conformity, homogeneity, MUs, and gradient index were found at collimator angles of 20° and 30°. Additionally, OAR sparing was favorable at these angles. Based on target coverage, homogeneity, and MUs, the collimator angles were optimized for VMAT planning. Conclusion: Our findings offer valuable guidance to clinical medical physicists in making informed decisions regarding collimator angles. The dosimetric analysis underscores the importance of selecting the optimal collimator angle for accurate PTV coverage.

Keywords

• dose-volume histogram
• collimator angle
• head and neck carcinoma
• planning target volume
• volumetric-modulated arc therapy