DISEASE CHARACTERISTICS: Histologically confirmed newly diagnosed glioblastoma multiforme requiring radical radiotherapy No anaplastic astrocytoma or low-grade astrocytoma Able to start radiotherapy within 5 weeks of definitive surgery (unless delay due to cause other than medical illness or poor performance status)

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: See Disease Characteristics Karnofsky 60-100% Life expectancy: Not specified Hematopoietic: WBC at least 3,000/mm3 Granulocyte count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hepatic: AST and ALT no greater than 2 times upper limit of normal (ULN) Bilirubin no greater than 2 mg/dL PT and aPTT no greater than 1.5 times ULN Renal: Creatinine less than 1.5 mg/dL Cardiovascular: No severe cardiac disease Pulmonary: No severe lung disease Other: No other significant life-threatening disease No other active malignancy No known glucose-6-phosphate dehydrogenase deficiency No known porphyria Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY: Biologic therapy: No biologic therapy for at least 4 weeks after study completion No immunotherapy for at least 4 weeks after study completion Chemotherapy: No chemotherapy for at least 4 weeks after study completion Endocrine therapy: Concurrent steroids allowed Radiotherapy: See Disease Characteristics No prior radiotherapy for this disease or other brain tumor No prior radiotherapy to face, head, or neck Surgery: See Disease Characteristics Recovered from prior surgery or postoperative complication Other: At least 48 hours since prior MRI scan with contrast No concurrent MRI scans with contrast No other concurrent experimental drug