Evaluation of outcomes after stereotactic radiosurgery for pilocytic astrocytoma

Pilocytic astrocytomas are rare intracranial gliomas that are typically treated with surgical extirpation. Our aim was to report the radiologic and clinical outcomes of patients treated with stereotactic radiosurgery (SRS) for pilocytic astrocytoma in the primary and salvage setting. Patients with pilocytic astrocytoma treated at a single institution with SRS from 1990 to 2015 were reviewed. Patient, disease, and treatment characteristics were collected and overall survival, local control, and toxicity were evaluated. Twenty-eight consecutive patients (12 females and 16 males) with a median age of 17.4 years at SRS were identified. Overall, 46% of patients were treated with SRS as part of the initial treatment course after biopsy or subtotal resection, and the remainder as a salvage therapy. The most common location was the cerebellum (28%) followed by brainstem and basal ganglia (21 and 18%, respectively). Four patients received prior external beam radiation therapy (14%). Median tumor volume was 1.84 cc (0.19-15.94 cc), and 39% had a cystic component at SRS. Prescription dose ranged from 4 to 20 Gy (median 16 Gy) to a median isodose line of 50% (range 30-100%). With a median follow-up of 5.2 years (0.3-17.1 years), all patients remained alive at last follow-up. Two patients demonstrated evidence of local radiographic progression at last follow-up (7%). No toxicity could be directly attributed to SRS. In this SRS series, durable tumor control was achieved in 93% of patients with pilocytic astrocytoma, although continued follow up will be important giving the natural history of this disease. As demonstrated, SRS is an appropriate technique in the primary and recurrent treatment of pilocytic astrocytoma that offers favorable disease control and infrequent clinical toxicity.