509 Modern Hearing Preservation Outcomes After Vestibular Schwannoma Stereotactic Radiosurgery

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INTRODUCTION: For patients with vestibular schwannoma (VS), stereotactic radiosurgery (SRS) has proven effective in controlling tumor growth, while hearing preservation remains a key goal. METHODS: During the years 2013-2018, 353 patients underwent Gamma-knife surgery for VS at our institution. We followed 175 patients with pre-SRS serviceable hearing (Gardner-Robertson Score, GR 1 and 2). Volumetric and dosimetry data were collected, including Biological Effective Dose (BED), integral doses (ID) of total and intra-canalicular (IC) tumor components and hearing outcomes. RESULTS: Mean age was 56 years, 74 (42%) had baseline GR of 2, and mean cochlear dose was 3.5 Gy. Time to serviceable hearing loss (GR 3-4) was 38 months (95% CI, 26-46), with 77% and 62% hearing preservation in the 1st and 2nd years. Patients optimal for best hearing outcomes were younger than 58 with baseline GR of 1, free canal space 0.041cc (diameter of 4.5 mm) and mean cochlear dose <3.1 Gy. For such patients, hearing preservation rates were 92% by 12 months and 81% by 2 years, staying stable for >5 years post-SRS, significantly higher than the rest of the population. CONCLUSIONS: Hearing preservation after SRS for VS patients with serviceable hearing is correlated to the specific baseline GR score (1 or 2), age, cochlear dose and BED. Increased tumor-free canal space correlates with better outcomes. The most durable hearing preservation correlates with factors commonly associated with smaller tumors away from the cochlea.

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