Object The response rate of vestibular schwannomas (VSs) to radiosurgery has reached the 97% level in several published series. When failure rarely occurs, some controversy has existed as to whether the tumor has to be resected or can be safely retreated with radiosurgery. The authors retrospectively studied the outcome of retreating 11 patients with Gamma Knife surgery (GKS). Methods The authors studied 11 patients at the New England Gamma Knife Center who had undergone GKS as a second radiosurgical treatment for VS from 1994 to 2007. One patient underwent proton-beam radiotherapy as the first treatment, and the other 10 patients had undergone GKS initially. Tumor control (size before and after the first and the second treatment) was evaluated using MR imaging to demonstrate the course after the 2 treatments. Facial nerve function (House–Brackmann grading system), trigeminal nerve function, hearing (Gardner–Robertson classification), and any adverse radiation effects were evaluated. The prescription dose was 12 Gy (11–13.2 Gy) for both treatments. Results Of the 11 patients, 2 showed increase, 1 had no change, and, in 8, the VS decreased in size after the retreatment. One tumor remained unchanged over the first 6 months, but demonstrated signs of internal necrosis. All patients demonstrated stable facial nerve function. Regarding facial numbness, 2 patients experienced increases, 8 no change, and 1 decreased numbness. There was no functional hearing prior to the second treatment in 10 patients, and hearing was impaired in 1 patient. Adverse radiation effects (slight peduncular edema) were seen in 2 patients after the second treatment, and 1 patient had edema after the first treatment as well. Conclusions Vestibular schwannomas can be retreated with GKS with good tumor control response and low risk of toxicity.

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