Hearing preservation for acoustic neuromas after treatment with hypo-fractionated radiosurgery

Purpose/Objective: Hearing preservation remains an important treatment outcome in pts undergoing therapy for acoustic neuromas. A high degree of tumor control while preserving the function of the fifth, seventh, and eighth cranial nerve and avoiding harm to the adjacent brain stem is crucial. Materials/Methods: Recently analyzed are pts undergoing a hypo-fractionated 2000cGy radiosurgery protocol. Hearing outcome based upon four or five fractions treated over either consecutive days or alternate or more days was analyzed. 162 pts followed a median of 26 months (range 6–96 months) were evaluated for pure-tone audiometry and speech discrimination. All pts received 2000cGy in four or five fractions. Initially, pts with tumors larger than 3cm received five fractions of 400cGy on alternate or more days. Pts with less than 3cm tumors received 500 rad times 4 fractions on alternate or more days. Based upon radiobiological data, and in certain cases patient preference; the schedule was abbreviated to treat consecutive days. Thus, there were four treatment groups. 24 pts receiving 500x4 on consecutive days (median tumor size=1.2cm), 47 pts receiving 500x4 on alternate or more days (median tumor size=1.5cm), 3 pts receiving 400x5 on consecutive days (median tumor size=3.5cm), and 88 pts receiving 400x5 on alternate or more days (median tumor size=2.1cm). Pts hearing was evaluated by pure-tone audiometry as part of the follow-up process, which included MRI scans of the IACs with gadolinium enhancement. Results: The pts who received 400 rad × 5 on alternate or more days had a hearing preservation rate of 85%. This is defined as maintaining hearing after treatment or having an improvement. Pts receiving 500 rad × 4 on alternate or more days had a hearing preservation rate of 77%. Preservation of hearing was less in pts receiving consecutive day treatment. The pts that received 400 rad × 5 on consecutive days had a hearing preservation rate of 67%, and those receiving 500 rad × 4 on consecutive days had a rate of 71%. Those who received 500 rad on alternate or more days had a mean follow-up of 40 months while the 400 × 5 on consecutive days had a mean follow-up of 26 months, and 500 × 4 treated on consecutive days had a 30 month mean follow-up. When the 400 rad × 5 group was compared to the other three groups for statistical analysis there was found to be a near statistically significant improvement in hearing (p=0.08). Conclusions: This data evaluating treatment sequence using hypo-fractionated stereotactic radiosurgery for treatment of acoustic neuromas would suggest that fraction size and sequence of treatment (alternate day or greater) has a profound effect on hearing. The group receiving 400 × 5 fractions treated on alternate or more days had the greatest hearing preservation. This suggests that the benefits to hearing are durable and of great benefit to pts.