RADT-25. PROTON THERAPY FOR YOUNG ADULT MEDULLOBLASTOMA: ACUTE TOXICITY AND DISEASE CONTROL OUTCOMES

Abstract

Abstract BACKGROUND Report disease control, survival outcomes, and acute radiotherapy related toxicity among young adult medulloblastoma patients who received proton craniospinal irradiation (CSI) as part of multimodality therapy. We reports the completion rates of planned adjuvant chemotherapy. METHODS All adult medulloblastoma patients (≥ 22 years old) who received postoperative proton CSI +/- chemotherapy at our institution between 2008 and 2020 were included. Patient, disease, and treatment details along with prospectively obtained patient-reported acute CSI toxicities were collected (CTCAE v3 or v4). Acute hematologic data were analyzed. RESULTS Twenty young adult medulloblastoma patients were included. The median age at diagnosis was 27 years (range, 22–30). 45% had high-risk disease. 75% received chemotherapy, most of whom (65%) received post-CSI chemotherapy. Eight patients (40%) received concurrent vincristine with CSI. The median CSI dose was 36 GyE (range, 23.4-36) with a median tumor bed boost of 54 GyE (54-55.8). The median duration of radiotherapy was 44 days (range, 40-49). There were no acute ≥ grade 3 gastrointestinal or hematologic toxicities attributable to CSI (during or within 4 weeks after completion of RT). Grade 2 nausea and vomiting affected 25% and 5% of patients, respectively. Acute grade 2 hematologic toxicity affected 36% of patients. Among patients planned to receive adjuvant chemotherapy (n=13), 100% completed at least 4 cycles and 85% completed all planned chemo cycles. With a median follow-up of 3.1 years, 4-year actuarial local control, DFS, and OS were 90% (95% CI 53-99), 90% (95% CI 53-99), and 95% (95% CI 72-99), respectively. Two patients had disease recurrence, both with local failures in the high dose boost volume in the tumor bed. CONCLUSIONS Proton radiotherapy for CSI in young adult medulloblastoma patients is well tolerated and shows promising disease control and survival outcomes. These data support the standard use of proton CSI for adult medulloblastoma.