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.