RONC-02. Clinical outcome after craniospinal irradiation with pencil beam scanning proton therapy for children and young adults/adolescents with brain tumors

BACKGROUND: Craniospinal irradiation (CSI) is an essential treatment component to achieve cure for some brain tumors in children and young adults/adolescents (C-AYAs). Multimodal treatment approaches are however associated with treatment-related late toxicities in these developing patients. Pencil beam scanning proton therapy (PBSPT) allows for a minimization of dose delivered to organs at risk and the brain integral dose and, thus, potentially also a reduction of radiation-induced adverse events. We report the clinical outcome and toxicity rates after CSI for C-AYAs treated with PBSPT. METHODS: We reviewed 71 C-AYAs with a median age of 7.4 years (1.7 – 21.3) who received CSI with PBSPT. Medullobastoma (n=42, 59%) and ependymoma (n=8, 11%) were the most common histologies. Thirty-four (48%) patients presented with metastatic disease at diagnosis. Sixteen (23%) patients were treated for tumor recurrence/progression and 9 (13%) patients underwent re-irradiation. Median prescribed total dose was 54 GyRBE (18 – 60.4) and median craniospinal dose 24 GyRBE (18 – 36.8). Toxicities were recorded according to CTCAE v5.0. RESULTS: With a median follow-up time of 24 months (2 – 195), 12 (17%) patients died due to progressive disease. Eight (11%) patients experienced local failure and 15 (21%) distant failure after PBSPT. Estimated 2-year OS, LC and DC was 86.9%, 86.0% and 80.4%, respectively. Grade 3 acute toxicity (thrombocytopenia, neutropenia, nausea) was observed in 5 (7%) patients. Late grade 3 toxicities (stroke, cataract and CNS necrosis) were observed in 3 (4%) patients, 8, 9 and 16 months after PBSPT, respectively. One (1%) patient developed grade 4 CNS necrosis 8 months after CSI. Late grade ≥3 toxicity free rate was 92.3% at 2 years. No radiation-induced secondary cancer was observed. CONCLUSION: Excellent tumor and brain/spinal distant control and a low late grade ≥3 toxicity rate after CSI were observed in our cohort of C-AYAs treated with PBSPT.