Novel Targeted Radiotherapy in Pediatric Patients With Inoperable Relapsed or Refractory HGG

Inclusion Criteria: * Previously confirmed (histologically or cytologically) high grade glioma that is clinically or radiographically suspected to be relapsed, refractory, or recurrent * ≥ 10 years of age and ≤ 25 years of age at time of consent/assent * If ≥ age 16 years, Karnofsky performance status of ≥ 60. If \< age 16 years, Lansky performance status ≥ 60 * Platelets ≥ 75,000/μL (last transfusion, if any, must be at least 1 week prior to study registration, and, unless deemed medically necessary, no transfusions are allowed between registration and dosing) * Absolute neutrophil count ≥ 750/μL * Hemoglobin ≥ 8 g/dL (last transfusion must be at least 1 week prior to study registration, and, unless deemed medically necessary, no transfusions are allowed between registration and dosing) * Using the bedside Schwartz formula, estimated GFR (creatinine clearance) \> 60 ml/min/1.73m2 * Alanine aminotransferase \< 3 × ULN * Bilirubin \< 2 × ULN * At least 1 measurable intracranial lesion with longest diameter of at least 10 mm on any imaging sequence. * Patients with previously known neurological deficits must be clinically stable at time of enrollment and able to complete all study related procedures. Patients with documented or newly diagnosed neurological deficits will be enrolled at the investigator's discretion. * If patient receives steroids for neurological symptom control, the dose must be stable (unchanged for three weeks prior to registration) or on a steroid tapering …