Dosimetric analysis of beam number variations in IMRT for head-and-neck, breast, and pelvic cancers using Halcyon

Abstract

This study investigated the dosimetric effects of varying beam numbers (9, 11, and 13) in intensity-modulated radiation therapy (IMRT) using the Halcyon linear accelerator at ShingMark University Hospital. IMRT plans for 27 patients with head-and-neck, breast, and pelvic cancers were evaluated according to the RTOG 0615 protocol, focusing on Planning Target Volume (PTV) dose coverage, uniformity, maximum and minimum doses, and Organ-at-Risk (OAR) dose constraints. For breast cancer, the 11-beam plan improved PTV coverage (V50Gy: 97.9 ± 0.5 %) and reduced maximum dose compared to 9- and 13-beam plans, while the 13-beam plan lowered heart mean dose by up to 10.5 % in left breast cases. In pelvic cases, the 13-beam plan enhanced OAR sparing, reducing bowel V35Gy by 10.5 % compared to the 9-beam plan, with minimal PTV coverage differences (<0.2 %). For head-and-neck cancer, the 13-beam plan improved PTV D95 % and spared critical structures like the brainstem, though it increased doses to the chiasm and cochlea. Treatment time and Monitor Units rose with more beams, particularly for head-and-neck and pelvic cases, but remained minimal for breast cases. These findings suggest tailoring beam numbers to cancer type and clinical priorities, balancing dosimetric benefits with treatment efficiency.