Hearing Preservation in Vestibular Schwannoma Radiosurgery.

Background: Our aim was to evaluate hearing outcomes in vestibular schwannoma (VS) patients treated by stereotactic radiosurgery (SRS) in the modern era of cochlear-dose restriction, providing information about patient and tumor characteristics, radiosurgery dosimetry, and effects on functional preservation. Methods: During the years 2013-2018, 353 patients underwent Gamma-knife SRS for VS at our institution. We followed 175 VS patients with pre-SRS serviceable hearing (Gardner-Robertson Score, GR 1 and 2) and at least 3 years of follow-up. Volumetric and dosimetry data were collected at SRS and 6 months later, Biological Effective Dose (BED), integral doses (ID) of total and intra-canalicular (IC) tumor components, cochlear doses and hearing outcomes. Results: Mean age was 56 years and 74 (42%) had baseline GR of 2. The majority of cases were Koos 2 (47%), and 15% were Koos 3-4. Mean cochlear dose was 3.5 Gy. Overall, median time to hearing deterioration of at least 1 level in the GR scale was 31 months (95% CI 23,42), with 72% keeping their baseline GR level in the 1st year, 55% in the 2nd year, and 46% in the 3rd year. In a multivariable analysis, the risk for hearing deterioration at any time point was significantly higher in patients with baseline GR of 2 (OR=2.24, p=0.025). Predictors of lower risk for hearing deterioration included tumor volume <0.43 cc (OR=0.43, p=0.027) and BED < 61 (OR=0.44, p=0.047). The risk for earlier hearing deterioration was significantly reduced by age< 58 (HR=0.54, p=0.009), mean cochlear dose <3.1 Gy, (HR=0.56, p=0.002) and BED <61 (HR=0.45, p=0.002), while it was higher when the tumor-free canal space was <0.041cc (HR=1.88, p=0.008). Median time to serviceable hearing loss (GR 3-4) was 38 months (95% CI, 26-46), with 77% hearing preservation in the 1st year, 62% in the 2nd year, and 50% in the 3rd year. Patients optimal for the best hearing outcomes would be younger than 58 with baseline GR of 1, free canal space 0.041 cc (diameter of 4.5 mm) and mean cochlear dose <3.1 Gy. For such patients, serviceable hearing preservation rates were 92% by 12 months and 81% by 2 years, staying stable for more than 5 years post-SRS. Conclusion: Hearing preservation after SRS for VS patients with pre-treatment serviceable hearing is correlated in the current era to the specific baseline GR score (1 or 2), age, cochlear dose and BED. Increased baseline tumor-free canal space correlates with better hearing outcomes. [ABSTRACT FROM AUTHOR]