Inclusion Criteria

DISEASE CHARACTERISTICS:

- Radiologically and clinically suspected solitary glioblastoma multiforme

- High-grade disease

- Agreed to undergo stereotactic biopsy as part of routine diagnostic work-up

PATIENT CHARACTERISTICS:

- WHO performance status 0-2 (0-1 for patients ≥ 65 years old)

- Life expectancy > 4 months

- Hemoglobin ≥ 9.0 g/dL

- Neutrophil count ≥ 1.5 x 10^9/L

- Platelet count ≥ 100 x 10^9/L

- Serum bilirubin ≤ 1.5 times upper normal of limit (ULN)

- AST ≤ 1.5 times ULN

- Uncorrected EDTA-Isotope creatinine clearance ≥ 40 mL/min

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use two forms of effective contraception 4 weeks prior to,
during, and for 6 months after completion of study therapy

- Able to cooperate with procedures and follow-up

- Not at high risk of complications from blood-brain barrier disruption with mannitol
on pre-treatment CT scan (an open quadrigeminal plate cistern, absence of dilatation
of the contralateral frontal horn, and absence of uncal herniation)

- No history of uncontrolled seizures

- No phenylketonuria

- No current or previous malignancies at sites other than the brain, except for
adequately treated cone-biopsied carcinoma in-situ of the uterine cervix or basal
cell or squamous cell carcinoma of the skin

- Not at high medical risk due to nonmalignant systemic disease, including active
uncontrolled infection

- No known hepatitis B, hepatitis C, or HIV positivity by serology

- No concurrent congestive heart failure, history of NYHA class III-IV cardiac disease,
history of myocardial infarction or active ischemic heart disease within the past
year, or history of cardiac arrhythmia or thromboembolic disease

- No other condition that, in the investigator's opinion, would not make the patient a
good candidate for the clinical trial

PRIOR CONCURRENT THERAPY:

- At least 12 hours since prior and no concurrent steroids

- At least 48 hours since prior phenylalanine-containing drinks (e.g., colas)

- At least 48 hours since prior excessive consumption of phenylalanine-containing
foods, including any of the following:

- Low phenylalanine content (e.g., fruit juice, fruits [except bananas],
vegetables, and low-protein breads and pastas

- Medium phenylalanine content (e.g., corn, bread, french fries, potatoes, peas,
rice, and regular pasta)

- High phenylalanine content (e.g., refried beans, chicken, nuts, hamburgers,
peanuts, cheese, eggs, pork chops, steak, bananas, and milk)

- At least 4 weeks since prior major thoracic and/or abdominal surgery and recovered

- No prior cranial radiotherapy

- No prior endocrine therapy, immunotherapy, or chemotherapy for the brain tumor

- No other concurrent anticancer therapy or investigational drugs