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

Abstract

PurposeTo 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 methodsBetween 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 14Gy. Sustained changes ⩾2mm in any diameter were deemed significant, and useful hearing was defined as inter-aural pure tone average (PTA)⩽50dB. Possible prognostic factors for hearing retention were tested by dividing the patients at pre-specified cutpoints: age (60years), maximum tumour diameter (20mm), initial PTA (20dB) and dose (12 vs 14Gy). ResultsEighty-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 65mo (range 10–184mo). Eighty-two (97.6%) were controlled, the remaining two requiring salvage surgery for progression at 5.75 and 9.75years. Also, one of the post-operative cases required surgery at 2.1years after SRS. For the 50 sporadic primary SRS patients with initially useful hearing, median age was 56 (range 21–76), median initial PTA 16dB (range −11 to +45dB) and median tumour diameter 21mm (range 10–33mm). Four received 14Gy, the rest 12Gy. After SRS, 19 patients (38%) retained useful hearing. The Kaplan–Meier estimated preservation rate at 5years was 50% (95% CI 36–64%) but by 10years, 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⩾20dB was 5.0 (95% CI 2.2–11.2) times that with PTA<20dB. ConclusionsTumour 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 10years.