DISEASE CHARACTERISTICS: Histologically confirmed supratentorial * grade I/II glioma, including: Diffuse fibrillary astrocytoma No pilocytic astrocytoma No mixed tumor with ependymoma elements * Supratentorial sites include: Frontal, temporal, parietal, or occipital lobes Thalamus, basal ganglia, or midbrain Lateral or third ventricles Pons, medulla, or optic chiasm tumors allowed only if secondary to eligible tumor More than 1 separate tumor allowed Diagnosis based on surgical biopsy or subtotal resection Measurable or evaluable disease on T2-weighted MRI required

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-2 Hematopoietic: WBC greater than 3,500/mm3 Platelet count greater than 130,000/mm3 Hemoglobin greater than 9 g/dL Hepatic: Bilirubin less than 2 times upper limit of normal (ULN) AST less than 2 times ULN Alkaline phosphatase less than 2 times ULN Renal: Creatinine less than 1.5 times ULN Other: No active or uncontrolled infection No second malignancy within 3 years except: Nonmelanomatous skin cancer In situ cervical cancer No pregnant or nursing women Negative pregnancy test required within 7 days prior to entry Effective contraception required of fertile patients

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No prior chemotherapy Endocrine therapy: At least 1 week since prior steroids OR Stable steroid dose for at least 1 week prior to study Radiotherapy: No prior cranial or head and neck irradiation Surgery: See Disease Characteristics