Results of linear accelerator-based stereotactic radiosurgery for recurrent and newly diagnosed acoustic neuromas

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Abstract
Stereotactic radiosurgery (SRS) is used to treat acoustic neuromas, but additional information is needed to firmly establish its safety and efficacy. We review our experience over 7 years treating 29 consecutive patients with a modified linear accelerator (linac) SRS system. Between August 1989 and October 1995, 29 patients with a median age of 67 years (range 26 to 83) underwent linac SRS treatment. Twenty‐five patients had unilateral acoustic neuromas, and four patients with neurofibromatosis type II had bilateral vestibular schwannoma. Eligibility criteria for SRS were recurrent tumors (n = 9), age >65 (n = 16), or patient preference (n = 6). Follow‐up magnetic resonance imaging scans were performed on all patients. The most common presenting symptoms were hearing impairment (18 patients) and gait difficulties (17 patients). Ten patients were deaf in the affected ear prior to treatment. Doses to the periphery of the tumor ranged from 800 to 2,400 cGy (median 1,600 cGy) prescribed to the 50% to 80% isodose line (median 80%). After a median radiographic follow‐up of 49 months (range 4 to 110 months), 11 tumors were smaller, 17 were stable, and one had evidence of progression (at 41 months). The 5‐year local disease control rate (Kaplan‐Meier estimate) was 94%. Acute complications were minimal, with only two patients experiencing nausea and vomiting after the procedure. Long‐term complications included new or progressive trigeminal and facial nerve deficits with estimated 5‐year incidences of 15% and 32%, respectively. Subjective hearing reduction or loss occurred in 14 (74%) of the 19 patients who had useful hearing prior to treatment. Five patients died from unrelated causes. These results suggest that linac SRS provides excellent short‐term tumor control rates. Since there was a high risk of cranial nerve neuropathy, we do not recommend using only computed tomography‐based planning and high prescription doses. Int. J. Cancer (Radiat. Oncol. Invest.) 90, 145–151 (2000).