VMAT plan quality comparison between Clinac-iX and halcyon treatment delivery systems for nasopharyngeal carcinoma.

ABSTRACT

Radiotherapy planning for nasopharyngeal carcinoma is a complex process due to the proximity of critical structures. Volumetric modulated arc therapy (VMAT) can improve the therapeutic ratio. However, multiple treatment delivery systems offer VMAT with varying technical specifications. This study compares the dosimetric plan quality of 2 systems, Clinac-iX and Halcyon in nasopharyngeal carcinoma. We utilized contrast-enhanced computed tomography (CECT) simulation and magnetic resonance (MR) image datasets from thirty patients with nasopharyngeal carcinoma to contour target volumes and organs at risk (OARs). Two medical physicists independently performed dosimetric planning for Clinac-iX and Halcyon machines, following standard international dosimetric constraints for OARs. We compared plan quality for dosimetric profiles, indices, and plan complexity parameters from both machines. Dosimetric coverage for target volumes and plan quality indices, such as homogeneity, conformity, and coverage, showed no significant differences between Clinac-iX and Halcyon. However, Halcyon demonstrated significantly better OAR sparing, particularly for the spinal cord, optic chiasm, lenses, eyeballs and lower brain volume integral dose (BVID) (p < 0.05). Complexity parameters showed that both systems used a similar number of arcs, but Halcyon had higher monitor units and lower treatment time per fraction owing to higher dose rate. Our study results favor Halcyon for better plan quality regarding critical organ sparing, low brain volume integral dose, and fast treatment delivery. This study can be used as a reference for selecting an optimal treatment delivery system for nasopharyngeal carcinoma patients in centres equipped with multiple linear accelerators.