Intrathecal Busulfan in Treating Patients With Recurrent, Refractory, or Metastatic Leptomeningeal Tumors

DISEASE CHARACTERISTICS: Histologically confirmed neoplasm that is metastatic in the cerebrospinal fluid or leptomeningeal/subarachnoid space Cytologic diagnosis of malignancy in the cerebrospinal fluid or neuroimaging evidence of leptomeningeal tumor by MRI Must have a recurrent or refractory leptomeningeal tumor Leptomeningeal tumors of leukemia, lymphoma, and all germ cell tumors must have also failed initial treatment or be recurrent No evidence of obstructive hydrocephalus or complete block of the spinal cerebrospinal fluid pathways on prestudy technetium Tc 99m albumin or indium In 111 DTPA flow study PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Karnofsky 60-100% Life expectancy: At least 8 weeks Hematopoietic: Absolute neutrophil count greater than 1,500/mm^3 Platelet count greater than 100,000/mm^3 Hepatic: Bilirubin less than 2.5 mg/dL SGOT or SGPT less than 1.5 times normal Renal: BUN less than 30 mg/dL Creatinine less than 1.5 mg/dL Calcium within normal limits Neurological: Neurological examination stable No rapidly progressing or deteriorating neurological deficits Other: No active infectious process Magnesium, phosphorus, potassium, chloride, and bicarbonate normal Not pregnant or nursing Fertile patients must use effective contraception PRIOR CONCURRENT THERAPY: Biologic therapy: At least 4 weeks since prior immunotherapy Chemotherapy: At least 6 weeks since prior nitrosoureas or mitomycin At least 4 weeks since any other prior chemotherapy At least 3 weeks since prior intrathecal chemotherapy No other concurrent intrathecal chemotherapy Endocrine therapy: For patients on corticosteroids: Must be on a stable dose of corticosteroids for at least 1 week Radiotherapy: At least 3 weeks since prior radiotherapy to the CNS At least 4 weeks since any other prior radiotherapy No concurrent radiotherapy to the CNS Surgery: At least 3 weeks since prior surgery Other: No concurrent medication that may interfere with study results (e.g., immunosuppressive agents other than corticosteroids)