Chemotherapy and Radiation Therapy After Surgery in Treating Children With Newly Diagnosed Astrocytoma, Glioblastoma Multiforme, Gliosarcoma, or Diffuse Intrinsic Pontine Glioma

RATIONALE: Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die. Radiation therapy uses high-energy x-rays to damage tumor cells. Giving chemotherapy together with radiation therapy may kill more tumor cells. PURPOSE: This phase II trial is studying how well giving chemotherapy together with radiation therapy after surgery followed by chemotherapy alone works in children with newly diagnosed astrocytoma, glioblastoma multiforme, gliosarcoma, or diffuse intrinsic pontine glioma.

OBJECTIVES: * Compare the event-free survival of patients with newly diagnosed anaplastic astrocytoma, glioblastoma multiforme, gliosarcoma, or diffuse intrinsic pontine glioma (DIPG) treated with adjuvant temozolomide administered concurrently with postoperative radiotherapy and then alone as maintenance therapy vs historical control cohorts treated in prior Pediatric Oncology Group and Children's Cancer Group studies. * Determine the toxicity of this regimen in these patients. * Determine the efficacy of this regimen in patients with DIPG. * Determine the toxicity of this regimen in patients with DIPG. OUTLINE: This is a multicenter study. * Adjuvant chemoradiotherapy: Beginning within 6 weeks after surgical resection or diagnosis\*, patients without gross residual disease undergo cranial irradiation 5 days a week for 6 weeks. Beginning within 6 weeks after surgical resection, patients with gross residual disease undergo radiotherapy as above followed by boost radiotherapy for 1 week. All patients receive oral temozolomide once daily beginning within 5 days after initiation of radiotherapy and continuing for a total of 6 weeks in the absence of disease progression or unacceptable toxicity. * Adjuvant maintenance therapy: Beginning 4 weeks after completion of adjuvant chemoradiotherapy, patients receive oral temozolomide on days 1-5. Treatment repeats every 28 days for a total of 10 courses in the absence of disease progression or unacceptable toxicity. NOTE: \*For patients with diffuse intrinsic pontine glioma only Patients are followed every 3-6 months for 4 years and then annually thereafter. PROJECTED ACCRUAL: A total of 50-60 patients will be accrued for this study within 12-14 months.