Integration test of biaxially rotational dynamic-radiation therapy for nasopharyngeal carcinoma: Efficacy evaluation and dosimetric analysis.

Abstract

OXRAY is a new O-ring-shaped radiotherapy system delivering biaxially rotational dynamic-radiation therapy (BROAD-RT), a technique that enables non-coplanar volumetric-modulated arc therapy (VMAT) for large target volumes without requiring couch movement. The purpose of this study was to evaluate the benefits of BROAD-RT and to perform an integration test to confirm the plan deliverability and its accuracy from the treatment planning system to OXRAY for patients with nasopharyngeal carcinoma. We compared treatment plans for BROAD-RT and coplanar VMAT (COVMAT) created in RayStation for 15 patients with nasopharyngeal cancer using the Wilcoxon signed-rank test. P values less than 0.05 were considered statistically significant. Additionally, we confirmed the plan delivery accuracy of BROAD-RT from the treatment planning system to OXRAY; gamma passing rates (GPRs) and delivery time were evaluated. The criteria for pass and fail were ≥95 % at γ3%2 mm. BROAD-RT significantly improved the homogeneity and conformity index of planning target volume and reduced dose volume indices compared with COVMAT in D_{0.03 cc} for the brainstem, D_{0.03 cc} for the left optic nerve, D_{0.03 cc} for the brachial plexus, D_mean for each submandibular gland, D_mean for the oral cavity, and D_mean for each parotid gland. All plans for BROAD-RT passed the integration test; the mean GPR (3 %/2 mm) was above 95 % and the median delivery time was 209 s. BROAD-RT delivered by OXRAY passed the integration test, and it demonstrated the potential benefit of improving the dose distribution compared with COVMAT for patients with nasopharyngeal carcinoma.