Proton-Based Re-Irradiation of Locally Recurrent Pediatric Brain Tumors in Close Proximity to the Brainstem

PURPOSE: Local recurrence of aggressive, pediatric brain tumors remains a challenge. We offered full-course re-irradiation with proton therapy (PT) to children with local failures in proximity to the brainstem.

PATIENTS AND METHODS: Eleven children (7 male, 4 female) underwent fractionated re-irradiation using pencil beam-based PT for local recurrence following maximum prior multidisciplinary treatment for ependymoma (N = 6), atypical teratoid rhabdoid tumor (N = 3), papillary tumor of the pineal region (N = 1) and atypical meningioma (N = 1).Median age at first radiotherapy (RT) was 4.5 years (range: 1.5-14.8); at re-RT was 6.7 years (range: 3.0-18.9); median interval between courses was 21 months (range: 13-160). In 9/11 children Gross Tumor was identifiable.Primary RT was with photons (N = 6) or protons (N = 5). Re-RT planning was based on cumulative dose summation. Permissible re-RT OAR doses were individualized. Median prescription dose was 54.0 Gy(RBE) (range 44.0-54.0). All re-treatments were delivered at 1.8-2.2 Gy(RBE) per fraction. A constant RBE value of 1.1 was used.

RESULTS: At median follow-up of 42.5 months (range 7-63), 9 /11 children (82%) achieved local control. Actuarial 2- and 3-year local control and overall survival rates were 89% and 76%, and 82% and 73%, respectively.Strategies of balancing target dose with OAR considerations resulted in a median cumulative brainstem surface dose (D0.1cc) of 81.5 Gy(RBE) (range: 65.8-99.48). No CNS toxicities ≥ Grade 2 were observed, specifically no symptomatic brainstem or brain necrosis.

CONCLUSION: Selective re-irradiation with pencil beam-based proton radiotherapy, using specifically modified treatment planning approaches, can be effective and safe, even in cases with tumor abutting the brainstem.