Radiosurgery for acoustic neurinomas (vestibular schwannomas)

Background: Radiosurgery is a therapeutic technique characterized by the de livery of a single high dose of ionizing radiation from an external source to a precisely defined intracranial target. The application of radiosurgery to the treatment of acoustic neurinomas has increased substantially in the last decade. Most of the published experience pertains to the use of the g amma knife. Objectives: To report the experience at the first Israeli Linear Accelerato r Radiosurgery Unit in the management of 44 patients with acoustic neurinom as. Methods: We analyzed the clinical records and imaging studies of all patien ts undergoing radiosurgery for acoustic neurinomas between 1993 and 1997, a nd quanitified the changes in tumor volume, hearing status, and facial and trigeminal nerve function. The contribution of radiation dose and original tumor volume upon those variables was also studied. Results: At a mean follow-up of 32 months (range 12-60), 98% of the tumors were controlled (75% had shrunk; 23% had stable volume). The actuarial hear ing preservation rate was 71%. New transient facial neuropathy developed in 24% of the patients, persisting in mild degrees in 8%. Neuropathy correlat ed primarily with tumor volume. Tumors with volumes >4 mi were at high risk when marginal radiation doses were >1,400 cGy. Dose reduction to a maximum of 1,400 cGy produced no neuropathies in the last 20 patients, still prese rving tumor control rates. Conclusions: Radiosurgery is an effective and cost-efficient therapeutic mo dality for newly diagnosed acoustic neurinomas in the elderly or medically infirm population, and for all residual or recurrent tumors after conventio nal surgery.