496 Impact of the Mean Cochlear Biologically Effective Dose on Hearing Preservation After Stereotactic Radiosurgery for Vestibular Schwannoma

Abstract

INTRODUCTION: Stereotactic radiosurgery (SRS) is a useful alternative for small to medium size vestibular schwannoma (VSs). METHODS: This is a retrospective longitudinal single center study. Were analyzed 213 patients with useful baseline hearing. Risk of hearing decline was assessed for GR classes and pure tone average (PTA) loss. Mean follow-up period was 39 months (median 36, 6-84). RESULTS: Hearing decline (GR class) 3 years after SRS was associated with higher cochlear BEDGy2.47 mean (OR 1.39, p = 0.009). BEDGy2.47 mean was more relevant compared to BEDGy2.47 max (OR 1.13, p = 0.04). Mean (p = 0.91) and maximal (p = 0.66) cochlear doses were not statistically significant. Risk of PTA loss (continuous outcome, follow-up minus baseline) was significantly corelated with BEDGy2.47 mean at 24 (beta coefficient 1.55, p = 0.002) and 36 (beta coefficient 2.01, p = 0.004) months after SRS. Mean (p = 0.27) and maximal (p= 0.87) cochlear doses were not significant. Risk of PTA loss (> 20 dB versus <=20) was associated with higher BEDGy2.47 mean at 6 (OR 1.36, p= 0.002), 12 (OR 1.36, p = 0.007) and 36 (OR 1.37, p = 0.02) months. Mean cochlear dose was statistically significant only at 24 months. Risk of hearing decline at 36 months for BEDGy2.47 mean of 7-8, 10 and 12 Gy2.47 was 28%, 57% and 85%, respectively. CONCLUSIONS: Cochlear BEDGy2.47 mean is relevant for hearing decline after SRS and more relevant as compared with BEDGy2.47 max. Three years after SRS, this was sustained for all hearing decline evaluation modalities. Our data suggests BEDGy2.47 mean cut-off of <= 8 Gy2.47 for better hearing preservation rates.