Carmustine Implants and O(6)-Benzylguanine in Treating Children With Recurrent Malignant Glioma

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