DISEASE CHARACTERISTICS: Histologically proven grade IV astrocytoma or glioblastoma multiforme confined to 1 or both hemispheres of the brain Confirmation of histology by NIH neuropathology review required MRI or CT completed within 3 weeks of initial evaluation No clinically apparent leptomeningeal metastases No uncontrolled seizures despite standard anticonvulsant therapy No history of epilepsy diagnosed a year or more before glioblastoma

PATIENT CHARACTERISTICS: Age: Over 18 Performance status: Karnofsky 80-100% OR ECOG 0-1 Life expectancy: More than 3 months Hematopoietic: WBC at least 3,500/mm3 Absolute granulocyte count at least 900/mm3 Platelet count at least 100,000/mm3 Hemoglobin at least 10 g/dL No hematologic disease requiring treatment Hepatic: Liver function tests no greater than 2.5 times upper limit of normal No hepatic disease requiring treatment Renal: Creatinine no greater than 1.3 mg/dL OR Creatinine clearance at least 95 mL/min No renal disease requiring treatment Cardiovascular: No history of hospitalization or medication for: Cardiovascular disease with LVEF 45% or less Myocardial infarction Arrhythmia Coronary artery disease Angina Congestive heart failure Stroke No thromboembolic disease requiring treatment Pulmonary: No history of hospitalization or medication for chronic obstructive pulmonary disease or asthma Other: No peptic ulcer disease or inflammatory bowel disease within the past 2 years No documented history of intolerance to methylxanthines (e.g., allergic or serious adverse reactions) No history of psychiatric or medical illness that would preclude therapy No other malignancy within the past 5 years except basal cell skin cancer or carcinoma in situ of the cervix No contraindication to serial CT or MRI (e.g., logistical problems, noncompliance, contrast allergies) Not pregnant or nursing Negative pregnancy test

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No prior chemotherapy Endocrine therapy: Not specified Radiotherapy: No prior radiotherapy Surgery: Prior biopsy or subtotal or near-total resection allowed At least 7-10 days but no more than 3 months since prior surgery and/or biopsy Other: No recent methylxanthine-containing medications No concurrent anticoagulants or methylxanthines (e.g., aspirin, nonsteroidal antiinflammatory drugs, warfarin, heparin, theophylline, aminophylline, theobromine) for preexisting medical conditions