External Beam Radiation Therapy and Cetuximab Followed by Irinotecan and Cetuximab for Children and Young Adults With Newly Diagnosed Diffuse Pontine Tumors and High-Grade Astrocytomas

Inclusion Criteria: * Patients must have either (1) histologic proof of a high-grade astrocytoma reviewed by a POETIC institutional pathologist or (2) a radiological diagnosis via MRI scan of a typical diffuse pontine tumor made by a POETIC institutional neuroradiologist. Patients with a radiological diagnosis via MRI scan of a typical diffuse pontine tumor will be enrolled on the diffuse pontine tumor arm of the study regardless of histology in cases that are biopsied. Note: For collaborating non-POETIC institutions, the reviews may be done by an institutional pathologist/neuroradiologist. * Patients must begin study prescribed therapy within 42 days of neurosurgical resection or biopsy of the tumor (high-grade astrocytoma patients) or radiological diagnosis (diffuse pontine tumor patients). * Age ≥ 3-years and \< 22-years-old. * Brain MRI (and any other studies done according to clinical indications) must not show any definitive evidence of leptomeningeal or extra-neural metastases. * ANC ≥ 1000/μL and platelet count ≥ 100,000/μL * Patients must have adequate organ function as defined by: * Hepatic: total bilirubin \< 1.5 mg/dl, AST ≤ 2.5 x the upper limit of normal. * Renal: serum creatinine ≤ 1.5 x the upper limit of normal for age, or calculated creatinine clearance or nuclear GFR ≥ 70 ml/min/1.73 m2. * The patient, or for minors, a parent or legal guardian, must give informed written consent indicating they are aware of the investigational nature of this study. Exclusion Criteria: * Evidence of leptomeningeal or extra-neural metastatic disease. * Prior radiation therapy or chemotherapy * Pregnancy, mothers unwilling to refrain from breast-feeding, and sexually mature patients unwilling to practice an effective form of birth control. * Other significant concomitant medical illnesses that would compromise the patient's ability to receive all prescribed study therapy. * Prior therapy which specifically and directly targets the EGFR pathway. * Prior severe infusion reaction to a monoclonal antibody. * Significant history of uncontrolled cardiac disease; i.e., uncontrolled hypertension, unstable angina, recent myocardial infarction (within prior 6 months), uncontrolled congestive heart failure, and cardiomyopathy with decreased ejection fraction. * Patients with known Gilbert's Syndrome.