Gyroscopic Stereotactic Radiosurgery: A Retrospective Analysis

Introduction Stereotactic radiosurgery (SRS) is a safe and effective non-invasive treatment for both primary and secondary brain tumors. Recently, a gyroscopic frameless, self-contained, and self-shielded radiosurgery system has been clinically implemented. The device is equipped with a 2.7-MV linear accelerator, capable of delivering up to 1500 MU/minute, and onboard image guidance for initial setup and tracking. Herein, we present our institution's initial experience with this novel system. Methodology Between September 2020 and July 2023, 30 patients (77%) with brain metastases, 8 patients (20.5%) with benign skull base tumors, and 1 patient (2.5%) with an arteriovenous malformation were treated for a total of 107 lesions (1-11 lesions per patient) using 243 radiation fractions, with each patient receiving between 1 and 5 fractions. Results The median delivered fractional dose was 1350 cGy (range, 500-2,400 cGy) in 3 fractions (range, 1-5) for a total dose of 2,400 cGy (range, 1,200-3,500 cGy) prescribed to the 63% isodose line (range, 50%-85%). The median lesion volume was 1.1 cc (range, 0.04-28.04 cc). The median parametric values of conformity, homogeneity, and dose falloff were calculated: confidence interval (CI) = 1.43 (1.21-1.86), homogeneity index (HI) = 1.52 (1.14-2.00), and gradient index 50 (GI50) = 3.16 (2.49-4.88). Median treatment time was 24 minutes per lesion (range, 9-123 minutes), and median isocenters per lesion was 4 (range, 1-15), with a median of 74 beams per lesion delivered (range, 23-195). Acute toxicities were limited to 6 (16.2%) patients. Late toxicity was limited to seven lesions, causing radiation necrosis, five symptomatic, and one patient with a case of Bell's palsy. No grade 4+ toxicity was observed. At a median follow-up of 14.7 months (range, 2.4-46.3), local control was 95%. Conclusions This is among the largest gyroscopic radiosurgery clinical experiences published to date. The results show that local control and toxicity results align with historical control data for patients treated with other SRS modalities, demonstrating the functionality, performance efficiency, and dosimetric benefits of this new radiosurgery platform.