Stereotactic radiosurgery for pilocytic astrocytomas part 1: outcomes in adult patients.

To assess outcomes when stereotactic radiosurgery (SRS) is used during multimodality management of pilocytic astrocytomas in adult patients. Fourteen patients (six male and eight females) with pilocytic astrocytomas underwent SRS between 1994 and 2006. The median patient age was 32 years (range, 19-52 years). Initial surgical management included stereotactic biopsy (N = 4), gross total resection (N = 1), and partial resection (N = 9). Fractionated radiation therapy had failed in six patients. The median radiosurgery target volume was 4.7 cc (range, 0.6-33.7 cc) and the median margin dose was 13.3 Gy (range, 10-20 Gy). At a median follow-up of 36.3 months (range 6.1-109 months), three patients died and 11 were alive. The overall survival after SRS for the entire series was 100%, 88.9% and 88.9% at 1, 3 and 5 years, respectively. Localized solid tumor progression was seen in two patients. Cyst progression was noted in three of nine patients with cystic tumors and mixed solid and cyst progression was noted in two with cystic tumors. The progression free survival after SRS (including tumor growth and cyst enlargement) for the entire series was 83.9%, 31.5% and 31.5% at 1, 3 and 5 years, respectively. Prior surgical resection was associated with better progression free survival after SRS (P = 0.027). Despite their purported benign nature, pilocytic astrocytomas in adult patients often do not behave benignly. Unresectable pilocytic astrocytomas that are located in critical or deep areas of the brain require additional management approaches. In this preliminary experience obtained over a 12 year interval, SRS is most valuable for patients after maximal feasible surgical resection. Delayed cyst progression contributes to late loss of tumor control.