Hearing preservation after low dose linac radiosurgery for acoustic neuroma depends on initial hearing and time

Purpose: To assess long term outcomes and factors determining hearing preservation after low dose linac stereotactic radiosurgery (SRS) for acoustic neuroma (AN) at the Royal Adelaide Hospital using prospectively collected data.

Material and methods: Between 1994 and 2010, 102 patients had SRS for AN. Five patients had neurofibromatosis type 2, six sporadic cases had relapsed after surgery, and the remaining 91 sporadic cases had primary SRS. Dose was 12 or 14 Gy. Sustained changes ≥ 2 mm in any diameter were deemed significant, and useful hearing was defined as inter-aural pure tone average (PTA) ≤ 50 dB. Possible prognostic factors for hearing retention were tested by dividing the patients at pre-specified cutpoints: age (60 years), maximum tumour diameter (20mm), initial PTA (20 dB) and dose (12 vs 14 Gy).

Results: Eighty-four of the 91 sporadic primary SRS cases were evaluable for tumour control with at least one post-treatment MRI. Their median follow-up was 65 mo (range 10-184 mo). Eighty-two (97.6%) were controlled, the remaining two requiring salvage surgery for progression at 5.75 and 9.75 years. Also, one of the post-operative cases required surgery at 2.1 years after SRS. For the 50 sporadic primary SRS patients with initially useful hearing, median age was 56 (range 21-76), median initial PTA 16 dB (range -11 to +45 dB) and median tumour diameter 21 mm (range 10-33 mm). Four received 14 Gy, the rest 12 Gy. After SRS, 19 patients (38%) retained useful hearing. The Kaplan-Meier estimated preservation rate at 5 years was 50% (95% CI 36-64%) but by 10 years, this had fallen to 23% (95% CI 12-41%). On univariate analysis, the only significant factor was initial PTA (P < 0.0001). The estimated risk of hearing loss after SRS for patients with initial PTA ≥ 20 dB was 5.0 (95% CI 2.2-11.2) times that with PTA < 20 dB.

Conclusions: Tumour control was excellent (99/102=97% freedom from surgical salvage). Hearing preservation was strongly dependent on initial PTA, but there was a steady fall-off in hearing out to at least 10 years.