Dosimetric impact of VMAT delivery angles for early glottic cancer treatment

Masao Nakayama; Shuhei Sekii; Eiichi Miyazaki; Tomohiko Oya; Ryo Nishikawa; Moshi Geso

doi:10.1016/j.meddos.2024.04.001

Dosimetric impact of VMAT delivery angles for early glottic cancer treatment

Med Dosim. 2024 May 9:S0958-3947(24)00022-0. doi: 10.1016/j.meddos.2024.04.001. Online ahead of print.

Authors

Masao Nakayama¹, Shuhei Sekii², Eiichi Miyazaki³, Tomohiko Oya³, Ryo Nishikawa², Moshi Geso⁴

Affiliations

¹ Division of Radiation Therapy, Kita-Harima Medical Center, Ono, Hyogo 675-1392, Japan; Division of Radiation Oncology, Kobe University Graduate School of Medicine, Kobe City, Hyogo 650-0017, Japan; Discipline of Medical Radiations, School of Health and Biomedical Sciences, RMIT University, Bundoora, Victoria 3083, Australia. Electronic address: naka2008@med.kobe-u.ac.jp.
² Division of Radiation Therapy, Kita-Harima Medical Center, Ono, Hyogo 675-1392, Japan; Division of Radiation Oncology, Kobe University Graduate School of Medicine, Kobe City, Hyogo 650-0017, Japan.
³ Division of Radiation Therapy, Kita-Harima Medical Center, Ono, Hyogo 675-1392, Japan.
⁴ Discipline of Medical Radiations, School of Health and Biomedical Sciences, RMIT University, Bundoora, Victoria 3083, Australia.

PMID: 38729843
DOI: 10.1016/j.meddos.2024.04.001

Abstract

This study investigates the dosimetric effects of different gantry rotation angles used in volumetric modulated arc therapy (VMAT) for early glottic carcinoma. VMAT treatment plans using full-arc, half-arc, and partial-arc gantry rotation angles were generated from 22 computed tomography datasets of early-stage (T1-2N0) glottic laryngeal cancer. Dosimetric parameters associated with the planning target volume (PTV) and organs at risk (OARs), specifically the carotid arteries and thyroid, were compared. To assess the robustness of the VMAT plans, dose variations were analyzed by introducing positional shifts of 1, 3, and 5 mm from the isocenter of each plan along the superior-inferior, left-right, and anterior-posterior axes. Furthermore, we examined the size of the PTV, the air cavity volume within the PTV, and the variability of the beam path length through the gantry angles to investigate their correlations with PTV dose variations in the presence of positioning errors. Compared to full-arc and half-arc plans, the dosimetric parameters of partial-arc plans were found to be higher in PTV (D2%, D5%, D50%, and D_mean) and lower in OARs, while their dose variations of OAR parameters were greater for positioning errors. In addition, a correlation was observed between PTV size and PTV dose variations. Air cavity volume and depth variability were also correlated with some PTV parameters, depending on the arc plan. The results presented in this study suggest that the partial-arc gantry angles can allow higher PTV doses while minimizing OAR doses in VMAT treatment planning for early glottic cancer. However, the small delivery angles may lead to greater dose variations in the OARs when positioning errors occur.

Keywords: Glottic cancer; Head and neck cancer; Intensity modulated radiation therapy; Laryngeal cancer; Volumetric modulated arc therapy.