Dosimetric validation of biaxially rotational dynamic-radiation therapy using an O-ring linear accelerator.

BACKGROUND: Biaxially rotating O-ring linear accelerators equipped with biaxially rotating gantry-ring mechanics enable non-coplanar arc delivery without the need for couch rotation. This architecture is intended to achieve conformal dose distributions and enable efficient non-coplanar delivery compared with couch-rotated techniques. However, clinical implementation requires dosimetric verification to confirm delivery accuracy. This study aimed to validate the dosimetric accuracy and treatment efficiency of a biaxially rotating O-ring linac using AAPM Task Group (TG)-119 and TG-244 test cases, with reference to TG-218 acceptance criteria. MATERIALS AND METHODS: In this retrospective phantom-based dosimetric validation study, 26 treatment plans were generated in RayStation based on TG-119 and TG-244 and delivered as coplanar VMAT (cVMAT) or non-coplanar VMAT [dynamic swing arc (DSA)]. Point dose measurements were performed with an A1SL ionisation chamber, and dose distribution verification was conducted using the Delta4 Phantom+. Monitor units (MU) and beam-on time (BOT) were compared between cVMAT and DSA. RESULTS: All plans met the ±3% tolerance for absolute point-dose error (measured vs. calculated), with a mean error of -0.21% ± 1.09%. Gamma analysis (3%/2 mm, 10% threshold) showed a mean pass rate of 99.3%, exceeding the 95% threshold. Significant differences were observed in MU and BOT between cVMAT (median 862.4 MU, 104.0 s) and DSA (median 740.5 MU, 136.5 s). CONCLUSIONS: This study demonstrated dosimetric validation of a biaxially rotating O-ring linear accelerator using TG-119 and TG-244 test cases. The system achieved high accuracy in both cVMAT and DSA deliveries, supporting the dosimetric readiness for clinical implementation.