Abstract
PURPOSE: This study evaluated the usefulness of non-coplanar volumetric modulated arc therapy (VMAT) using a novel O-ring-type linear accelerator, OXRAY, in patients with prostate cancer (PCa). The focus was on those with the planning target volume (PTV) adjacent to the small or large intestine. MATERIALS AND METHODS: We enrolled 10 consecutive PCa patients with the PTV less than 10 mm from the small or large intestine. These patients underwent conventional coplanar VMAT (Conv-VMAT) using Halcyon, another O-ring-type linear accelerator, at our institute between July 2023 and July 2024. To evaluate the utility of OXRAY, we developed two simulation plans: biaxially rotational dynamic radiation therapy (BROAD-RT) and swing-fixed non-coplanar VMAT (SF-VMAT). A total dose of 63 Gy in 21 fractions was prescribed for all plans. Dosimetric parameters of the PTV and organs at risk were compared among the three plans using paired t-tests. RESULTS: No significant differences in the dose received to 95% of the volume (D95) of the PTV were observed among the three plans. However, the D95 of the PTV-base, defined as the three cranial slices of the PTV, significantly improved in BROAD-RT compared to Conv-VMAT, adhering to dose constraints of the small or large intestine. On the other hand, the improvement in SF-VMAT was insignificant. BROAD-RT and SF-VMAT significantly improved rectal dose indices compared to Conv-VMAT. CONCLUSION: For PCa patients with the PTV close to the small or large intestine, non-coplanar VMAT using OXRAY may improve the PTV-base coverage and decrease rectal dose compared to conventional VMAT plans, while adhering to dose constraints of the small or large intestines.