RecruitingPhase 1Radiation therapyLET Optimized IMPT in Treating Pediatric Patients With EpendymomaThis phase I trial studies the side effects of linear energy transfer (LET) optimized image modulated proton therapy (IMPT) in treating pediatric patients with ependymoma. Radiation therapy such as LET optimized IMPT, uses proton beams to kill tumor cells and shrink tumors without damaging surrounding normal tissues.