Audiological assessment before and after fractionated stereotactic irradiation for vestibular schwannoma

Purpose: To find the audiological outcome after LINAC-based fractionated st ereotactic irradiation (STI). Materials and methods: Twenty-four patients with vestibular schwannoma trea ted by fractionated STI between 1991 and 1997 had measurable hearing before STI and were followed audiologically for more than 6 months. The pure tone average (PTA) was measured by averaging the air-conduction threshold for f ive main frequencies (250-4000 Hz) before and periodically after STI in the 24 patients. Several possible prognostic factors for hearing preservation (defined as a PTA change at the last follow-up of less than 10 dB) were inv estigated. The median follow-up time was 22 months, ranging from 5 to 69 mo nths. The irradiation schedule was 36 Gy in 20 fractions in 5 weeks to 44 G y in 22 fractions in 6 weeks followed by 4 Gy/1 fraction boost. Results: The pure tone average before STI was distributed from 7 to 73 dB. Fifty percent of patients showed a change in PTA of less than 10 dB, 79.2% of patients showed a change in PTA of less than 20 dB and 20.8% of patients showed a change in PTA of more than 21 dB at the last follow-up. Only one patient (4%) became deaf. Cases with a sudden loss of hearing were more lik ely to experience hearing preservation than those with gradual loss of hear ing (P < 0.05). The mean age was younger in patients whose hearing was pres erved (P < 0.05). Poor pretreatment PTA appeared to linearly correspond to the changes in PTA (regression coefficient 0.78). The size of the tumor was not related to the change in PTA. No relationship was observed between the maximum or peripheral dose and the PTA change. The real benefit of stereot actic boost after small-field fractionated irradiation was not certain. Conclusion: Fractionated STI produced a hearing preservation rate compatibl e with meticulously collimated multi-spots single fraction irradiation. Fur ther follow-up is required to confirm the long-term benefits of fractionati on. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.