Radiation Therapy or Temozolomide in Treating Patients With Gliomas

DISEASE CHARACTERISTICS: * Histologically confirmed low-grade glioma, including any of the following types: * Astrocytoma (gemistocytic, fibrillary, or protoplasmatic) * Oligoastrocytoma * Oligodendroglioma * WHO grade II disease * Supratentorial tumor location only * RTOG neurological function 0-3 * Not a candidate for surgical treatment alone * Requires treatment, as determined by ≥ 1 of the following criteria: * Age ≥ 40 years * Radiologically-proven progressive lesion * New or worsening neurological symptoms other than seizures only (e.g., focal deficits, signs of increased intracranial pressure, or mental deficits) * Intractable seizures, defined by both of the following criteria: * Experiences persistent seizures that interfere with everyday life activities except driving a car * Failed 3 anti-epileptic drug regimens, including ≥ 1 combination regimen * Tumor material (paraffin-embedded) or histopathologic slides available PATIENT CHARACTERISTICS: Age * 18 and over Performance status * WHO 0-2 Life expectancy * Not specified Hematopoietic * Absolute neutrophil count ≥ 1,500/mm\^3 * Platelet count ≥ 100,000/mm\^3 Hepatic * No chronic hepatitis B or C infection * Bilirubin ≤ 1.5 times upper limit of normal (ULN) * AST or ALT ≤ 2.5 times ULN * Alkaline phosphatase ≤ 2.5 times ULN Renal * Creatinine ≤ 1.5 times ULN Other * Not pregnant or nursing * Fertile patients must use effective contraception during and for 6 months after completion of study treatment * No known HIV positivity * No other serious medical condition * No other prior or concurrent malignancy except surgically cured carcinoma in situ of the cervix or nonmelanoma skin cancer * No psychological, familial, sociological, or geographical condition that would preclude study participation * No medical condition that would preclude receiving oral medication (e.g., frequent vomiting or partial bowel obstruction) PRIOR CONCURRENT THERAPY: Biologic therapy * No concurrent growth factors for elevating absolute neutrophil counts for the purpose of temozolomide administration * No concurrent epoetin alfa * No concurrent immunotherapy or biologic therapy Chemotherapy * No prior chemotherapy * No other concurrent chemotherapy, including adjuvant chemotherapy for patients randomized to undergo radiotherapy Endocrine therapy * Not specified Radiotherapy * No prior radiotherapy to the brain * No concurrent integrated boost with intensity-modulated radiotherapy Surgery * Recovered from prior surgery * No concurrent surgical tumor debulking Other * No prior randomization to this study * No other concurrent investigational drugs * No concurrent regular use of agents known to be radiosensitizers or radioprotectors (e.g., cyclooxygenase-2 inhibitors, thalidomide, or amifostine) during study radiotherapy * Occasional use of nonsteroidal anti-inflammatory drugs for pain allowed