(0921) Does Radiation to the Semicircular Canals During Radiosurgery for Vestibular Schwannoma Affect Dizziness?

Introduction: Despite the strong association of cochlear dose and hearing loss during stereotactic radiosurgery (SRS) for vestibular schwannoma (VS), the association between semicircular canal (SCC) dose and balance outcomes has yet to be extensively characterized. The present study aims to correlate SCC radiation dose to post-procedural vestibular symptoms in patients with sporadic VS.

Methods: A retrospective chart review was performed on adults with sporadic VS treated via single-fraction SRS at a tertiary academic skull base referral center between 1999 and 2021. Univariable logistic regression was performed to predict vestibular symptoms based on the dose administered to the SCCs. Patient-reported dizziness, imbalance, nausea, vertigo, and tinnitus were evaluated as a binary result at most recent follow-up.

Results: A total of 40 patients were included, with an average follow-up of 4.7 ± 3.3 years and tumor size of 19.3 ± 3.9 mm. Median treatment volume, maximum dose, mean SCC dose, and maximum SCC dose were 1.4 ± 1.6 cm3, 24.7 ± 1.5 Gy, 4.6 ± 1.4 Gy, and 12.6 ± 4.1 Gy, respectively. There was no correlation of treatment volume, maximum dose, mean SCC dose, or max SCC dose with dizziness (p = 0.5542, 0.5868, 0.1183, 0.808; respectively), nausea (p = 0.7968, 0.5596, 0.1983, 0.6695; respectively), vertigo (p = 0.7636, 0.6901, 0.2176, 0.6855; respectively), or tinnitus (p = 0.92, 0.0921, 0.0776, 0.4567; respectively). There was no correlation of treatment volume or maximum dose with imbalance (p=0.7381, 0.1691; respectively); however, mean and max SCC dose did approach significance (p = 0.0802, 0.0828; respectively).

Conclusions: In patients with medium-sized VS receiving SRS, SCC dose was not correlated with vestibular outcomes, potentially pointing to a long-term, slow decline in vestibular function with adequate contralateral compensation. The effects of SRS dose on post-procedural outcomes in the setting of VS should be further investigated with objective testing to assess risk of long-term morbidity.