Author: Tetsuo Fukuda, Hideaki Hirashima, Kohei Kawata, Yukako Kishigami, Takashi Mizowaki, Mitsuhiro Nakamura, Yohei Sawada, Maika Urago 👨🔬
Affiliation: Kyoto University, kyotoUnivercity, Hitachi high-tech, Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University 🌍
Purpose: To present the comprehensive commissioning results of the O-ring shaped linac, OXRAY.
Materials and Methods: OXRAY enables a novel three-dimensional unicursal noncoplanar irradiation method called “Dynamic SwingArc” (DSA) synchronizing gantry-ring rotation. The available X-ray energies are 6 MV and 6 MV FFF. Fields are shaped only with multi-leaf collimator (MLC). Percentage depth dose and off-center ratio (OCR) data were acquired using 3D water phantom with source-to-surface distance of 100 cm. MLC-shaped square fields ranging from 20 to 200 mm were evaluated. OCR measurements were conducted at depths of 15, 100, and 200 mm. The measured data were compared with calculated data generated by the RayStation 2023B treatment planning system. Patient specific quality assurance (PSQA) was performed for 30 volumetric modulated arc therapy plans with trajectory of coplanar, non-coplanar and DSA. PSQA was evaluated using gamma pass rate (GPR) with criteria of 3%/2 mm criterion. Furthermore, the image guidance systems (kV-X-ray image and kV-cone beam computed tomography) were assessed using anthropomorphic phantoms. Localization accuracy (LA) was determined by comparing the differences between the initial position images and the corresponding image translated by pre-determined offsets.
Results: The differences between measured and calculated data were within the tolerance limits defined in the ESTRO Booklet 7. The PSQA analysis showed an average GPR exceeding 95%, meeting the acceptance criteria outlined in AAPM TG-218. LA was within 0.5 mm for translations and 0.5° for rotations, respectively, with no significant difference observed between the image guidance systems.
Conclusion: The OXRAY demonstrated acceptable beam quality for clinical application and accurately delivered prescribed doses. Additionally, the automatic image fusion functionality achieved high accuracy and precision in patient positioning, ensuring reliable implementation for image guided radiation therapy.