Radiosurgery for acoustic neurinomas (vestibular schwannomas)

Background: Radiosurgery is a therapeutic technique characterized by the delivery 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 gamma knife. Objectives: To report the experience at the first Israeli Linear Accelerator Radiosurgery Unit in the management of 44 patients with acoustic neurinomas. Methods: We analyzed the clinical records and imaging studies of all patients undergoing radiosurgery for acoustic neurinomas between 1993 and 1997, and 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 hearing preservation rate was 71%. New transient facial neuropathy developed in 24% of the patients, persisting in mild degrees in 8%. Neuropathy correlated 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 preserving tumor control rates. Conclusions: Radiosurgery is an effective and cost-efficient therapeutic modality for newly diagnosed acoustic neurinomas in the elderly or medically infirm population, and for all residual or recurrent tumors after conventional surgery.