Abstracts

Gamma Knife radiosurgery (GKS) offers an alternative to open surgery for mesial temporal lobe epilepsy (MTLE), but its safety and efficacy are not well-established. We report the two year outcome on seizure remission and morbidities of a multicenter, prospective pilot study of GKS., Patients had unilateral MTLE as determined by standard presurgical evaluation. GKS, randomized to 20 Gy or 24 Gy comprising 5.0-7.5mL at the 50% isodose volume, was performed on mesial structures including the amygdala, hippocampus, and parahippocampal gyrus. Treatment plans were approved at a central site to insure uniformity of lesions. Patients and primary treating physicians were blinded to dose. Regular visits with seizure diaries were obtained for 3 months at presurgical baseline and postoperatively for every three months until 18m, then at 24m. Patients were counted as [ldquo]seizure-free[rdquo] if no seizures (excluding auras) occurred between visits 18m-24m. Any subject that was not available for analysis was considered not seizure-free., Of 40 planned enrollments, 30 qualified resulting in 13 subjects in the high dose and 17 in the low dose group. 1 patient was lost to follow-up soon after treatment. 1 subject in the low-dose group underwent standard lobectomy after not being seizure-free 24 months following treatment. 1 subject experienced papilledema that responded partially to dexamethasone and underwent temporal lobectomy. Reductions in seizure frequency were seen in the high-dose group at 3, 6, 15, 18, and 24 months and for the low-dose group at 12, 15, 18, and 24 months (Wilcoxon signed rank test). Thus, both groups showed significant reductions in seizures at approximately one year following treatment. The low-dose group showed a seizure-free response at 24 months of [sim] 60% and the high-dose group response was [sim] 80% at 24 months. Although there is a difference in the seizure-free rates for the two treatment groups, the Fisher[apos]s Exact Test using a 2-sided p value indicates that the difference in percentage seizure-free for the two groups is not statistically significant (p=0.1194), a conclusion limited by the low power to resolve differences between treatment groups. Rates of steroid treatment, new headaches, and visual field defects did not differ between dose or seizure-outcome groups., GKS may offer a safe and effective alternative to standard open surgery for unilateral MTLE. High-dose GKS may be more effective than low-dose without additional morbidity. Disadvantages of GKS include latency to seizure-freedom. Further work is required to determine which patients may benefit from GKS., (Supported by NIH R01 NS039280; Elekta AB (Stockholm, Sweden).)