DISEASE CHARACTERISTICS:

• Histologically confirmed progressive supratentorial anaplastic astrocytoma or glioblastoma multiforme
• No multifocal disease or leptomeningeal dissemination of tumor
• No evidence of tumor crossing midline
• Limited intraventricular involvement
• Measurable unilateral mass at least 10 mm by contrast-enhanced MRI
• Received prior involved-field radiotherapy as a component of prior therapy
• Amenable to and in need of significant debulking

PATIENT CHARACTERISTICS:

Age

• 3 to 21

Performance status

• Karnofsky 60-100% OR
• Lansky 60-100%

Life expectancy

• More than 8 weeks

Hematopoietic

• Absolute neutrophil count greater than 1,000/mm3*
• Platelet count greater than 100,000/mm3*
• Hemoglobin greater than 8 g/dL (transfusions allowed) NOTE: * Transfusion independent

Hepatic

• Bilirubin no greater than 1.5 times normal
• AST and ALT less than 3 times normal
• Albumin at least 2 g/dL
• No overt hepatic disease

Renal

• Creatinine clearance no greater than 1.5 times normal OR
• Glomerular filtration rate greater than 70 mL/min
• No overt renal disease

Cardiovascular

• No overt cardiac disease

Pulmonary

• No overt pulmonary disease

Other

• Neurological deficits must be stable for at least the past week
• No uncontrolled infection
• No known hypersensitivity to nitrosoureas or polyethylene glycol
• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy

• At least 6 months since prior bone marrow transplantation
• More than 2 weeks since prior colony-stimulating growth factors (e.g., filgrastim (G-CSF), sargramostim (GM-CSF), or epoetin alfa)

Chemotherapy

• No more than 2 prior cytotoxic chemotherapy regimens
• No more than 3 prior chemotherapy regimens total
• More than 3 weeks since prior myelosuppressive chemotherapy (6 weeks for nitrosoureas) and recovered
• Prior systemic carmustine (or other nitrosourea) allowed provided patient did not experience non-hematopoietic grade III/IV toxicity

Endocrine therapy

• Concurrent dexamethasone allowed if on a stable dose for at least the past week

Radiotherapy

• See Disease Characteristics
• At least 3 months since prior radiotherapy
• No prior craniospinal irradiation for metastatic disease

Surgery

• See Disease Characteristics
• Prior biopsy or cytoreductive surgery allowed

Other

• Concurrent anticonvulsants allowed
• No other concurrent anticancer or investigational drugs