Five-year outcomes following hypofractionated stereotactic radiotherapy delivered in five fractions for acoustic neuromas: the mean cochlear dose may impact hearing preservation.

Background: The aim of this study was to assess the clinical outcomes of acoustic neuromas (ANs) treated with hypofractionated stereotactic radiotherapy (hypo-FSRT) prescribed at a uniform dose.
Methods: Forty-seven patients with a unilateral AN were treated consecutively with hypo-FSRT between February 2007 and March 2012. Nineteen patients maintained a serviceable hearing status at the beginning of hypo-FSRT. The prescribed dose was 25 Gy delivered in five fractions per week to the isocenter, and the planning target volume was covered by the 80% isodose line.
Results: The median follow-up and audiometric follow-up periods were 61 and 52 months, respectively. The estimated tumor control rate at 5 years was 90% (95% CI 76-96). The existence of the cystic component before hypo-FSRT had a significantly worse impact on tumor control (p = 0.02). The estimated hearing preservation rates at 1, 3 and 5 years were 68% (95% CI 42-84), 41% (95% CI 20-62) and 36% (95% CI 15-57), respectively. A borderline significant difference was identified in the mean biological effective dose with an α/β value of 3 Gy (BED ₃ ) to the ipsilateral cochlea between the preserved hearing and hearing loss groups (19 Gy vs. 28 Gy) (p = 0.08).
Conclusions: Hypo-FSRT delivered in five fractions for unilateral ANs may achieve excellent tumor control with no severe facial or trigeminal complications. The mean BED ₃ in the cochlea may impact the hearing preservation rate. Therefore, the cochlear dose should be as low as possible.