Carboplatin, Temozolomide, and Filgrastim in Treating Patients With Newly Diagnosed or Recurrent High-Grade Glioma

DISEASE CHARACTERISTICS: * Histologically confirmed newly diagnosed glioblastoma multiforme or anaplastic astrocytoma * Residual tumor on postoperative MRI * Bidimensionally measurable disease PATIENT CHARACTERISTICS: Age: * Under 65 Performance status: * Karnofsky or Lansky 70-100% OR * ECOG 0-2 Life expectancy: * Not specified Hematopoietic: * Absolute neutrophil count at least 1,000/mm\^3 * Hemoglobin at least 8 g/dL (transfusion allowed) * Platelet count greater than 100,000/mm\^3 Hepatic: * Bilirubin less than 1.5 times upper limit of normal (ULN) * SGPT no greater than 3 times ULN Renal: * Age 5 years and under: Creatinine less than 1.2 mg/dL * Age over 5 to 10 years: Creatinine less than 1.5 mg/dL * Age over 10 to 15 years: Creatinine less than 1.8 mg/dL * Age over 15 years: Creatinine less than 2.4 mg/dL Cardiovascular: * No myocardial infarction within the past 6 months Other: * No other concurrent serious medical condition that would preclude study * Able to tolerate oral medications * No prior malignancy for which patient received prior chemotherapy or spinal irradiation * No history of severe allergic reaction to platinum-containing compounds * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception PRIOR CONCURRENT THERAPY: Biologic therapy: * At least 72 hours since prior filgrastim (G-CSF) Chemotherapy: * No prior chemotherapy * No other concurrent chemotherapy Endocrine therapy: * Concurrent steroids for tumor-related cerebral edema allowed * No concurrent corticosteroids for solely antiemetic purposes Radiotherapy: * No prior or concurrent radiotherapy Surgery: * Recovered from prior surgery * No concurrent surgery