O6-benzylguanine and Carmustine in Treating Children With Refractory CNS Tumors

DISEASE CHARACTERISTICS: * Histologically or cytologically proven CNS tumor that is refractory to conventional therapy or for which no effective therapy is known * Histological requirement may be waived for brainstem and optic gliomas * Stratum 2: No bone marrow involvement PATIENT CHARACTERISTICS: * Age: 21 and under * Performance status: Karnofsky 50-100% OR Lansky 50-100% * Life expectancy: At least 8 weeks * Absolute neutrophil count at least 1500/mm3 * Platelet count at least 100,000/mm3 (stratum 2: at least 125,000/mm3) * Hemoglobin at least 8 g/dL * Bilirubin less than 1.5 mg/dL * SGOT/SGPT no greater than 2.5 times normal * Creatinine or GFR normal for age * If required, DLCO must be 80% of normal and patient old enough to cooperate for DLCO test * Neurologic deficits must be stable for at least 2 weeks prior to study * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception during and for 6 months after study PRIOR CONCURRENT THERAPY: * At least 7 days since prior biologic therapy or immunotherapy and recovered * At least 6 months since prior bone marrow transplant (stratum 1 only) * At least 7 days since prior growth factors * No concurrent filgrastim (G-CSF) prophylaxis * Stratum 2: No prior bone marrow transplantation * At least 2 weeks since prior myelosuppressive chemotherapy (6 weeks for nitrosourea) and recovered * Stratum 2: No greater than 2 prior chemotherapy regimens * No prior nitrosourea therapy * If rec…