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

Abstract

Background and Purpose: 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. Methods and Materials: 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. Results: BROAD-RT significantly improved the homogeneity and conformity index of planning target volume and reduced dose volume indices compared with COVMAT in D₀.₀₃ [cc] for the brainstem, D₀.₀₃ [cc] for the left optic nerve, D₀.₀₃ [cc] for the brachial plexus, Dₘₑₐₙ for each submandibular gland, Dₘₑₐₙ for the oral cavity, and Dₘₑₐₙ 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. Conclusions: 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.