Gefitinib and Radiation Therapy in Treating Children With Newly Diagnosed Gliomas

Inclusion Criteria: * Tumor: * Phase I: newly diagnosed non-disseminated diffuse intrinsic brainstem tumor or newly diagnosed (diagnostic scan must be within 4 weeks prior to treatment initiation), incompletely resected supratentorial malignant glioma (anaplastic astrocytoma, glioblastoma multiforme or other high-grade glioma) (STMG); the STMG group must have residual tumor evident on postoperative MRI or CT * Phase II: only newly diagnosed non-disseminated diffuse intrinsic brain stem glioma patients are eligible * Performance status: Karnofsky or Lansky \>= 50% assessed within two weeks prior to registration * Prior/concurrent therapy: * Chemotherapy: no prior therapy allowed, including prior gefitinib treatment * Radiation therapy (XRT): no prior therapy allowed * Bone marrow transplant: none prior * Anti-convulsants: patients with brain stem glioma (BSG) receiving EIACD will not be eligible; patients with STMG will be eligible for this study even if they are receiving enzyme inducting anti-convulsant drugs (EIACD) and will be stratified by use of EIACDs * Growth factors: off all colony forming growth factor(s) \> 2 weeks prior to registration (G-CSF, GM-CSF, erythropoietin) * ANC \> 1,000/ul * Platelets \> 100,000/ul (transfusion independent) * Hemoglobin \> 8g/dl (may be transfused) * Patients may have bone marrow involvement by disease * Creatinine \< 2 x normal for age or GFR \> 70 ml/min/1.73m\^2 * Bilirubin \< 1.5 x normal institutional normal for ag…