Furukawa Experience Of Gamma Knife Radiosurgery For Vestibular Schwannoma

Keywords: vestibular schwannoma, gamma knife, radiosurgery, outcome, hearing function

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     Evaluate long-term efficacy and complication of Gamma Knife radiosurgery (GKRS) for vestibular schwannoma.
     One hundred seventy-two patients with unilateral vestibular schwannoma who have follow up information out of 212 patients treated between November 1991 and October 1999 at our site are included. There were 114 women and 58 men and their ages ranged from 24 to 79 years (mean 55.2). Forty-six patients had history of prior surgical removal. The volume of the tumor ranged from 0.15 to 20.2cc (mean 5.2 and median 4.0).
     The doses given to the margin ranged from 10 to 17Gy (mean 12.9) using mostly 50% isodose. In 86 patients follow up information 5 to 10 years and in 66 patients follow up information more than 10 years after GKRS were available. The average follow up period was 107 months.
     Surgical removal after GKRS was performed in 15 patients. In two patients, surgical removal was needed due to new cyst formation within and/or adjacent to the tumor after more than 10 years of good regression by GKRS. Eleven patients died during the follow up period and in which one death was due to bleeding from tumor and in another 3 patients death were related to management of hydrocephalus and salvage surgery. Kaplan-Meier analysis showed survival without salvage surgical removal 10 years and 15 years after GKRS was 84% and 72%. For the tumors less than 4cc, the value was 89%, 89% and for the tumors more than 10cc the value was 77% and 58% (P=0.05). Ventriculoperitoneal shunt was needed in 11 patients and all of them were performed within 3 years after GKRS. No permanent cranial nerve palsy other than cochlear, vestibular, trigeminal and facial nerve was observed except deterioration of visual acuity in one patient due to overlooked hydrocephalus. We have seen no malignant transformation in this series.
     This is a retrospective study.
     Long time follow up showed the efficacy and safety of Gamma knife radiosurgery for vesitibular schwannoma.
     On the other hand need for surgical removal more than 10 years after GKRS does exist. Lifetime follow up may be needed after GKRS.


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