Radiation Therapy, Temozolomide, and Irinotecan in Treating Patients With Newly Diagnosed Glioblastoma Multiforme

DISEASE CHARACTERISTICS: * Histologically confirmed newly diagnosed supratentorial glioblastoma multiforme by surgical biopsy or excision * No gliomas graded less than glioblastoma multiforme * No recurrent malignant gliomas * No tumor foci below the tentorium or beyond the cranial vault * Study therapy must begin ≤ 5 weeks after surgery PATIENT CHARACTERISTICS: Age * 18 and over Performance status * Zubrod 0-1 Life expectancy * At least 8 weeks Hematopoietic * Absolute neutrophil count ≥ 1,500/mm\^3 * Platelet count ≥ 100,000/mm\^3 * Hemoglobin ≥ 10 g/dL\* * Hematocrit ≥ 30%\* NOTE: \*Transfusion allowed Hepatic * Bilirubin ≤ 0.5 mg/dL * ALT or AST ≤ 2 times upper limit of normal Renal * Creatinine ≤ 1.5 mg/dL * BUN ≤ 25 mg/dL Other * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective double-barrier contraception during and for 2 months after study participation * No AIDS * No other malignancy within the past 5 years except nonmelanoma skin cancer or carcinoma in situ of the cervix or bladder * No other major medical illness or psychiatric impairment that would preclude study participation PRIOR CONCURRENT THERAPY: Biologic therapy * No concurrent sargramostim (GM-CSF) Chemotherapy * No other concurrent chemotherapy Endocrine therapy * Concurrent steroid therapy allowed provided patient is on a stable or decreasing dose for at least 2 weeks before study entry Radiotherapy * No prior radiotherapy to the head or neck resulting in overlap of radiotherapy fields * Prior radiotherapy for stage T1 glottic cancer allowed Surgery * See Disease Characteristics * Recovered from prior surgery Other * No enzyme-inducing antiepileptic drugs within 14 days before the initiation of irinotecan * Concurrent non-enzyme-inducing antiepileptic drugs allowed