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Vero4DRT enables Dynamic WaveArc (DWA) by continuous gantry rotation and O-ring skewing with a moving dynamic multi-leaf collimator without couch rotation (Figure). In previous work, our team identified a dosimetric advantage of novel volumetric modulated arc therapy (VMAT) featuring continuously varying non-coplanar trajectories, the DWA therapy for accelerated partial breast irradiation (APBI) and stereotactic body radiotherapy (SBRT) for spinal metastases. The upgraded treatment planning system allowed free editing of the DWA trajectories. This ‘modified track DWA’ has now been implemented, which enabled DWA therapy for APBI and spinal metastases on the actual device. We then performed a prospective study of this modified track DWA for APBI and spinal metastases. This report aimed to evaluate the feasibility of DWA therapy and acute adverse event rate.

A prospective feasibility study of APBI and spinal SBRT with DWA was conducted in our single institution from 2020 to 2022, following approval by our Institutional Ethical Review Board (jRCT1052200034). Patients with stage I–II breast cancer or spinal metastases without any other lesions outside the spine were eligible (Table). For APBI, the customised trajectory was set up to avoid collision and angles that would directly irradiate the heart and left anterior descending artery. In the cervical and upper lumbar spine, the trajectories were set to avoid the shoulders and kidneys, respectively. Prescribed doses were 38.5 Gy/10 fr for APBI and 27 Gy/3 fr for SBRT for spinal lesions. The primary endpoint was the protocol treatment completion rate, whose definition was the completion of the scheduled number of DWA with the patient-specific quality assurance (PSQA). The PSQA of DWA was performed using ArcCheck (Sun Nuclear Corp.), and the gamma analysis criterion of 5%/1 mm and 3%/3 mm was used for all plans. The secondary endpoint was the acute adverse event rate during the first 90 days after the start of irradiation. In APBI, non-coplanar three-dimensional conformal radiotherapy (3D-CRT) and coplanar VMAT treatment plans were created for comparison with the DWA plans, which were equal to or superior to that of the 3D-CRT and VMAT. For spinal lesions, treatment was performed with DWA when it was equal or superior to coplanar VMAT.

Twenty-five patients were enrolled in this trial, including 12 with left breast cancer and 13 with spinal metastasis. The median age was 67 (range, 42–85) years. In all 25 cases, no DWA plans were inferior to the 3D-CRT and VMAT plans in quality. Protocol treatment was completed by DWA, and the treatment plans were clinically irradiated without collision in all fractions. The mean of the average passing rates was over 95% for DWA, which met the PSQA criteria. There were no Grade 2 or higher acute adverse events.

The modified track Dynamic WaveArc therapy was feasible for APBI and spinal lesions, which allowed safe treatment in all patients with minimal acute adverse events.