Simon Lo, Presenter: Nothing to Disclose

Achilles J. Fakiris MD, Abstract Co-Author: Nothing to Disclose

Mark A. Henderson MD, Abstract Co-Author: Nothing to Disclose

Thomas C. Witt MD, Abstract Co-Author: Nothing to Disclose

Robert M. Worth MD, Abstract Co-Author: Nothing to Disclose

Robert D. Timmerman MD, Abstract Co-Author: Nothing to Disclose

To examine the efficacy and toxicity associated with the treatment of Vestibular Schwannoma (VS) with low dose Gamma Knife (GK)-based stereotactic radiosurgery (SRS).

Sixty-nine patients with unilateral VS were treated with GK-based SRS at Indiana University Medical Center. Initially, treatments were delivered on a Leksell Gamma Knife, model B. After 2002, patients were treated on a model C Leksell Gamma Knife. With local anesthetic and intravenous sedation, the patient was placed in the stereotactic head frame. A high resolution MRI was obtained for planning purposes and the VS was contoured as the target. Treatment was delivered using multiple isocenters in a single session to a mean dose of 13 Gy (range 12-15 Gy) prescribed to the 50% isodose line (one patient’s treatment was prescribed to the 55% isodose line, two to the 60% isodose line, and two to the 62% isodose line). Tumor volume ranged from 0.034 to 14.4 ml. Treatment volume ranged from 0.055 to 17.2 ml. Typical conformality index (treatment volume divided by tumor volume) ranged from 1.15 to 1.3 in most cases.

The average age at treatment was 57.8 years. 31 patients were male and 38 were female. 16 patients had previously undergone surgical resection (< 50% resection in two patients, 50-90% resection in six patients, and > 90% resection in five patients, with extent of surgery not documented in three patients). Five of these patients received GKR soon after surgery, while 11 received GKR for recurrent VS. With a median follow-up time of 27.17 months (range 5.1-96.5 months), out of the 69 patients treated, 3 (4%), 38 (55%), and 28 (41%) had tumor enlargement, stabilization and shrinkage, respectively. Time to tumor enlargement ranged from 27.2 to 39 months. The 3- and 5-year actuarial tumor control rates were 94.2% and 90.9%, respectively. Out of the 30 patients with at least 3 years of follow-up (median follow-up time: 63.3 months), only one patient (3.3%) had tumor enlargement. The 3- and 5-year actuarial tumor control rates were both 96.6%. Out of the 32 patients with useful hearing before treatment, 14 (43.8%) retained pretreatment hearing. The incidence of V and VII injury were low. One patient had transient V and VII nerve deficits that had resolved at the time of last follow up. Another patient had intermittent numbness and mild decreased sensation in one distribution of V. Another patient had a transient worsening of a V nerve deficit present at treatment that returned to baseline by last follow up. One patient experienced a persistent grade II VII nerve palsy.

High quality low dose GK-based SRS is efficacious for local control of VS. It is associated with a reasonable rate of hearing preservation and a low risk of V and VII nerve injury. Longer follow-up is required to determine the long-term efficacy and toxicity associated with this procedure.

Lo, S, Fakiris, A, Henderson, M, Witt, T, Worth, R, Timmerman, R, Low Dose Gamma Knife-based Stereotactic Radiosurgery for Vestibular Schwannoma.  Radiological Society of North America 2007 Scientific Assembly and Annual Meeting, November 25 - November 30, 2007 ,Chicago IL. http://archive.rsna.org/2007/6001676.html