Efficacy and safety of proton radiotherapy for progressive or surgically unfavorable adult pilocytic astrocytoma: a single-center experience.

PURPOSE: Progressive adult pilocytic astrocytoma is rare, and management of surgically unfavorable disease remains insufficiently defined. Given the favorable long-term prognosis of WHO grade 1 glioma, local tumor control must be balanced against late toxicity. This study evaluated the efficacy and safety of PRT in adults with pilocytic astrocytoma. METHODS: Fourteen adult patients with progressive or surgically unfavorable pilocytic astrocytoma treated with PRT at a single institution were retrospectively analyzed. Patient, tumor, treatment, radiographic, survival, and toxicity data were assessed. Radiographic response was evaluated using bidirectional T2-weighted measurements. Overall survival (OS), progression-free survival (PFS), and radiation-induced contrast enhancement (RICE)-free probability were estimated using Kaplan-Meier analysis. Toxicity was graded according to CTCAE. RESULTS: Median prescribed dose was 54.0 Gy(RBE). PRT was delivered as salvage treatment in 10 patients (71%) or primary therapy in 4 patients (29%). Tumors frequently involved anatomically complex regions, including the posterior fossa, ventricular and midline structures, the optic pathway, and the suprasellar compartment. At last follow-up, radiographic regression included complete response in 3, partial response in 7, and minor response in 2 of 14 patients. Estimated OS at 3 and 5 years was 100%, whereas estimated PFS was 83.3% at both time points. RICE occurred in 3 patients, with 3- and 5-year RICE-free probabilities of 76.2%. Toxicity was predominantly low grade, with no grade 4 or 5 events. CONCLUSION: PRT was associated with durable tumor control, marked radiographic regression, favorable survival, and acceptable toxicity in selected adults with progressive or surgically unfavorable pilocytic astrocytoma.