The efficacy and safety of stereotactic radiosurgery in Koos Grade I–II vestibular schwannomas: a single-center retrospective analysis

Abstract Introduction Vestibular schwannomas (VS) are benign tumors arising from the vestibular nerve, accounting for nearly 80% of cerebellopontine angle tumors. For Koos Grade I–II lesions, stereotactic radiosurgery (SRS) has emerged as a minimally invasive alternative to microsurgery, offering high tumor control rates and favorable functional outcomes. However, optimal patient selection, timing, and dose protocols remain debated. Here, we aimed to evaluate the efficacy and safety of SRS in Koos Grade I–II VS. Method A retrospective cohort study was conducted on 88 patients with Koos Grade I–II vestibular schwannomas treated with single-session SRS between January 2012 and December 2024. Data were extracted on demographics, tumor characteristics, treatment parameters, and follow-up outcomes. The primary endpoint was five-year actuarial radiographic tumor control, with secondary endpoints including hearing preservation, cranial nerve function, and toxicity. Kaplan–Meier and Cox regression were used for time-to-progression, while modified Poisson models with robust variance were used for binary outcomes. Results With a median follow-up of 60 months, five-year actuarial radiographic tumor control was 83% using the study’s prespecified > 10% volumetric increase criterion. Among 61 patients with baseline serviceable hearing, 50 (82.0%) retained Gardner–Robertson Class I–II hearing. Facial nerve function was preserved at House–Brackmann grade ≤ II in 85 of 88 patients (96.6%). Trigeminal neuropathy and CTCAE grade ≥ 2 toxicity each occurred in < 5% of the cohort. Tumor volume was associated with radiographic progression in the exploratory multivariable Cox model (HR 1.04 per cm 3 , p = 0.04). Conclusion Single-fraction SRS at 12–13 Gy provided favorable functional outcomes in Koos Grade I–II vestibular schwannomas, while the observed five-year radiographic tumor control rate of 83% was lower than many contemporary series. Because the retrospective progression definition did not separately adjudicate post-SRS pseudoprogression, tumor control may have been underestimated. These findings support SRS as a treatment option for selected small-to-medium vestibular schwannomas, with cautious interpretation of exploratory prognostic analyses and a need for standardized long-term follow-up.