A retrospective study by the MGH group reported outcomes of 59 adult patients with medulloblastoma treated with proton CSI. Gross total resection was achieved in 75%; median CSI dose was 30.6 GyRBE; and the median total dose was 54.0 Gy (RBE). This study reported the 5-year PFS and OS were 86.5% and 95.8%; 10-year PFS and OS were 83.9% and 90.7%, respectively. Most common grade ≥2 late toxicities were anxiety/depressive symptoms (30%), motor dysfunction (25%), and ototoxicity (22%). Higher posterior fossa radiation dose was associated with increased risk of late toxicity, including worse cognitive dysfunction (P = .05).