Hearing Preservation for Vestibular Schwannomas Treated with Stereotactic Radiosurgery or Fractionated Stereotactic Radiotherapy

Background: Vestibular schwannomas (VS) are benign intracranial neoplasms arising from the eighth cranial nerve. Recently, targeted radiation therapy (RT) has proved increasingly successful as a noninvasive treatment for VS with promising tumor control compared with microsurgery. Long-term hearing and related cranial nerve outcomes, however, have been disputed for the three current RT modalities: stereotactic radiosurgery (SRS), fractionated stereotactic radiotherapy (FSRT), and hypofractionated stereotactic radiotherapy (hypo-FSRT).

Methods: A retrospective electronic chart review was conducted for all patients with unilateral VS treated with primary RT at a single academic medical center between 2000 and 2017. Our primary outcome measure was preservation of serviceable hearing status in the affected ear at last follow-up. Secondary outcome measures included subjective presence of tinnitus, vertigo, and imbalance. Deterioration rates in outcome measures were compared by RT modality. Survival curves for outcome measures were then compared between RT modalities, and differences in median deterioration-free survival quantified using log-rank tests.

Results: Sixty patients were identified, consisting of 33 (55%) FSRT cases, 21 (35%) SRS cases, and 6 (10%) hypo-FSRT cases. Postoperative deterioration in serviceable hearing and tinnitus demonstrated significant differences across the three RT cohorts. The SRS cohort had higher baseline incidence of non-serviceable hearing and disequilibrium compared with the other cohorts prior to RT (p = 0.001 and p = 0.022, respectively), but no differences in baseline morbidity rates were observed for vertigo and tinnitus. Five-year tumor control rates were 95.2, 93.9, and 100% with SRS, FSRT, and hypo-FSRT, respectively.

Conclusion: Our series indicated an excellent tumor control rate in all the modalities. Our SRS cohort exhibited increased incidence and shorter time to hearing deterioration compared with FSRT and hypo-FSRT cohort. However, this result may have been influenced in part by higher baseline morbidity in the SRS cohort, in addition to institutional or physician-specific factors influencing choice of RT modality. Thus far, the FSRT and hypo-FSRT cohorts exhibited comparable overall outcomes; interestingly, however, onset of post-RT tinnitus was observed only with FSRT. Further well-controlled studies with larger sample size and longer follow-up are needed to more robustly compare outcomes, particularly after hypo-FSRT.