Significance of Cochlear Dose in the Radiosurgical Treatment of Vestibular Schwannoma: Controversies and Unanswered Questions

BACKGROUND: Cochlear dose has been identified as a potentially modifiable contributor to hearing loss after stereotactic radiosurgery (SRS) for vestibular schwannoma (VS). OBJECTIVE: To evaluate the association between computed tomography-based volumetric cochlear dose and loss of serviceable hearing after SRS, to assess intraobserver and interobserver reliability when determining modiolar point dose with the use of magnetic resonance imaging and computed tomography, and to discuss the clinical significance of the cochlear dose with regard to radiosurgical planning strategy. METHODS: Patients with serviceable pretreatment hearing who underwent SRS for sporadic VS between the use of Gamma Knife Perfexion were studied. Univariate and multivariate associations with the primary outcome of time to nonserviceable hearing were evaluated. RESULTS: A total of 105 patients underwent SRS for VS during the study period, and 59 (56%) met study criteria and were analyzed. Twenty-one subjects (36%) developed nonserviceable hearing at a mean of 2.2 years after SRS (SD, 1.0 years; median, 2.1 years; range 0.6-3.8 years). On univariate analysis, pretreatment pure tone average, speech discrimination score, American Academy of Otolaryngology-Head and Neck Surgery hearing class, marginal dose, and mean dose to the cochlear volume were statistically significantly associated with time to nonserviceable hearing. However, after adjustment for baseline differences, only pretreatment pure tone average was statistically significantly associated with time to nonserviceable hearing in a multivariable model. CONCLUSION: Cochlear dose is one of many variables associated with hearing preservation after SRS for VS. Until further studies demonstrate durable tumor arrest with reduced dose protocols, routine tumor dose planning should not be modified to limit cochlear dose at the expense of tumor control.