Fractionated stereotactic radiation therapy for vestibular schwannomas: Dosimetric factors predictive of hearing outcomes

Purpose: To determine dosimetric factors predictive of hearing loss in vestibular schwannoma (VS) patients treated with definitive fractionated stereotactic radiation therapy (FSRT), and to report tumor control, serviceable hearing preservation, and cranial nerve toxicities.

Methods and materials: We identified 45 patients (29 men and 16 women) with unilateral sporadic VS, who underwent definitive FSRT. All patients had serviceable hearing prior to treatment, defined as Gardner-Robertson Class 1 or 2. All patients underwent an audiogram before the start of treatment and serial audiometric assessments after treatment. The median audiometric follow-up time was 35.2 months (range, 5.0-89.7 months). Patients underwent a median of 4.5 (range, 1-9) posttreatment audiograms. The ipsilateral cochlea was contoured retrospectively, and dosimetric data were used to determine factors predictive of losing serviceable hearing. The median clinical follow-up time was 29.9 months (range, 1.5-83.6 months).

Results: At the time of the last audiometric follow-up, 62% of patients retained serviceable hearing. The actuarial 1-, 2-, and 3-year serviceable hearing preservation rates were 83%, 75%, and 51%, respectively. The estimated median time to loss of serviceable hearing was 42.2 months. On multivariate analysis, cochlear volume <0.15 mL (hazard ratio, 2.849; 95% confidence interval, 1.116-7.270; P = .029) and mean cochlear dose <4000 cGy (hazard ratio, 3.178; 95% confidence interval, 1.116-9.049; P = .030) were statistically significant variables associated with serviceable hearing preservation. The actuarial tumor control was 100%. Three of 39 patients (8%) developed hemifacial spasm after FSRT (House-Brackmann Grade 3), 2 of which completely resolved. No patients experienced deterioration in trigeminal nerve function after FSRT.

Conclusions: Fractionated stereotactic radiation therapy can provide excellent tumor control with acceptable clinical outcomes. The mean dose to the cochlea is highly predictive of the probability of maintaining serviceable hearing after FSRT.