Busulfan in Treating Children and Adolescents With Refractory CNS Cancer

DISEASE CHARACTERISTICS: Histologically confirmed CNS malignancy, including any of the following: Primary malignant brain tumor refractory to standard therapy and metastatic to the cerebrospinal fluid (CSF) or leptomeningeal subarachnoid space Recurrent or persistent leptomeningeal leukemia, lymphoma, or germ cell tumor refractory to conventional therapy In second or greater relapse CSF white blood count greater than 5 cells/mm3 with blasts on cytospin OR Evidence of leptomeningeal tumor by MRI No concurrent bone marrow disease No obstruction or compartmentalization of CSF flow on CSF flow study PATIENT CHARACTERISTICS: Age: 3 to 21 Performance status: Lansky 50-100% (under 10 years) Karnofsky 50-100% (10 to 21 years) Life expectancy: Greater than 8 weeks Hematopoietic: Absolute neutrophil count greater than 1,000/mm^3 Platelet count greater than 75,000/mm^3 Hepatic: Bilirubin normal for age ALT and AST less than 5 times upper limit of normal (ULN) No hepatic disease Renal: Creatinine no greater than 1.5 times ULN OR Glomerular filtration rate greater than 70 mL/min No renal disease Cardiovascular: No cardiac disease Pulmonary: No pulmonary disease Other: No uncontrolled infection Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: At least 3 weeks since prior myelosuppressive chemotherapy (6 weeks for nitrosoureas) At least 1 week since prior intrathecal chemotherapy (2 weeks for cytarabine) and recovered Evidence of subsequent disease progression Concurrent systemic chemotherapy allowed for recurrent disease after first course of treatment except for the following: Chemotherapy targeted at leptomeningeal disease Other phase I agent Any agent that significantly penetrates the CSF (e.g., high dose methotrexate greater than 1 g/m2, thiotepa, high dose cytarabine, fluorouracil, IV mercaptopurine, nitrosoureas, or topotecan) Any agent that causes serious unpredictable CNS side effects Endocrine therapy: Prior dexamethasone allowed with decreasing or stable dose at least one week before study Concurrent dexamethasone or prednisone with chemotherapy regimen allowed Radiotherapy: At least 1 week since prior focal irradiation to the brain or spine At least 8 weeks since prior craniospinal irradiation No concurrent cranial or craniospinal irradiation Surgery: Not specified Other: No other concurrent intrathecal or systemic therapy for leptomeningeal disease