RATIONALE: Monoclonal antibodies, such as rituximab, can locate cancer cells and either kill them or deliver cancer-killing substances to them without harming normal cells. Drugs used in chemotherapy, such as carboplatin, cyclophosphamide, etoposide, etoposide phosphate, and cytarabine, use different ways to stop cancer cells from dividing so they stop growing or die. Osmotic blood-brain barrier disruption uses certain drugs to open the blood vessels around the brain and allow anticancer substances to be delivered directly to the brain tumor. Chemoprotective drugs such as sodium thiosulfate may protect normal cells from the side effects of carboplatin-based chemotherapy. Combining rituximab with chemotherapy given with osmotic blood-brain barrier disruption plus sodium thiosulfate may kill more cancer cells.