Abstract

Background:

Prostate radiotherapy with pelvic nodal irradiation is challenging, particularly in elderly patients who have difficulty maintaining bladder filling and immobilisation during prolonged treatments. The Varian Halcyon system, with its 6 MV flattening filter-free beam, faster gantry rotation, higher multileaf collimator speed, and rapid imaging capabilities, may improve treatment accuracy and patient comfort. This study compares the dosimetric performance and delivery efficiency of IMRT, single-arc VMAT (SA-VMAT), and dual-arc VMAT (DA-VMAT) on the Halcyon platform.



Materials and Methods:

We retrospectively analyzed patients with localized prostate cancer and pelvic nodal involvement. IMRT, single-arc VMAT (SA-VMAT), and dual-arc VMAT (DA-VMAT) plans were created on an O-ring Halcyon linac using Eclipse v17 (Acuros XB). We evaluated target coverage, conformity, homogeneity, organ-at-risk (OAR) sparing, and delivery metrics (monitor units [MU], beam-on time, total time, modulation factor, gamma pass rate).



Results:

All techniques met target and OAR constraints. DA-VMAT showed superior conformity and homogeneity (PTV68 D95% = 99.89 ± 0.45; CI = 0.96 ± 0.01; HI = 0.063 ± 0.03) and improved rectal sparing (p < 0.05). DA-VMAT achieved higher D95% than SA-VMAT (p < 0.05); differences versus IMRT were not significant. SA-VMAT had the shortest beam-on time (1.55 min) and lowest MU, favouring workflow and potentially reducing discomfort. Both VMAT techniques reduced MU and beam-on time versus IMRT and improved delivery accuracy, with DA-VMAT yielding the highest gamma pass rate (99.3%).



Conclusion:

VMAT techniques improved efficiency over IMRT on Halcyon, while DA-VMAT offered better dosimetry for selected parameters. SA-VMAT enabled the fastest delivery and may benefit elderly or intolerance-prone patients. Technique selection should balance plan quality, delivery speed, and patient tolerance.



Keywords:



Prostate Cancer; Halcyon Linear Accelerator; Volumetric Modulated Arc Therapy; Intensity-Modulated Radiation Therapy; Radiotherapy Planning; Elderly Patients; Beam-On Time; Organ-at-Risk Sparing