Commissioning of an expanded-field radiation technique using a gimbal-mounted linear accelerator.

Abstract

Background and purposeA novel gimbal-mounted linear accelerator (linac) enables off-axis beam delivery. This study was aimed at commissioning an expanded-field radiation technique using a gimbal-mounted linac to validate beam data and implement patient-specific quality assurance (QA).Materials and methodsMeasurements were performed with gimbal head rotations of ±50.0 mm at the isocenter plane in both pan and tilt directions and were compared with the treatment planning system (TPS) calculation results. Percentage depth doses (PDDs) were obtained for multi-leaf collimator-shaped field sizes. Off-center ratios (OCRs) were measured at the depth of maximum dose (16 mm for 6 MV and 6 MV-FFF beams) and at depths of 50, 100, and 200 mm. For patient-specific QA, film-based measurements were conducted in patients with breast cancer involving axillary lymph nodes and esophageal cancer.ResultsFor the PDDs and OCRs, differences between the measured and TPS-calculated doses were maintained within ±2% inside the flattening region at all energy levels under gimbal head rotation. For patient-specific QA, gamma passing rates at 3%/2 mm exceeded 90% for each case.ConclusionsThese findings demonstrate that the proposed technique enables precise and effective off-axis beam delivery, thereby advancing the capabilities of modern radiotherapy.