Stereotactic radiosurgery for recurrent or unresectable pilocytic astrocytoma.

PURPOSE: To report the outcomes in patients with recurrent or unresectable pilocytic astrocytoma (PA) treated with Gamma Knife stereotactic radiosurgery (SRS). METHODS AND MATERIALS: Retrospective review of 18 patients (20 lesions) with biopsy-confirmed PA having SRS at our institution from 1992 through 2005. RESULTS: The median patient age at SRS was 23 years (range, 4-56). Thirteen patients (72%) had undergone one or more previous surgical resections, and 10 (56%) had previously received external-beam radiation therapy (EBRT). The median SRS treatment volume was 9.1 cm(3) (range, 0.7-26.7). The median tumor margin dose was 15 Gy (range, 12-20). The median follow-up was 8.0 years (range, 0.5-15). Overall survival at 1, 5, and 10 years after SRS was 94%, 71%, and 71%, respectively. Tumor progression (local solid progression, n = 4; local solid progression + distant, n = 1; distant, n = 2; cyst development/progression, n = 4) was noted in 11 patients (61%). Progression-free survival at 1, 5, and 10 years was 65%, 41%, and 17%, respectively. Prior EBRT was associated with inferior overall survival (5-year risk, 100% vs. 50%, p = 0.03) and progression-free survival (5-year risk, 71% vs. 20%, p = 0.008). Nine of 11 patients with tumor-related symptoms improved after SRS. Symptomatic edema after SRS occurred in 8 patients (44%), which resolved with short-term corticosteroid therapy in the majority of those without early disease progression. CONCLUSIONS: SRS has low permanent radiation-related morbidity and durable local tumor control, making it a meaningful treatment option for patients with recurrent or unresectable PA in whom surgery and/or EBRT has failed.