This phase II trial studies how well yttrium Y 90 ibritumomab tiuxetan and rituximab work in treating patients with recurrent or refractory primary central nervous system non-Hodgkin lymphoma. Radiolabeled monoclonal antibodies, such as yttrium 90 ibritumomab tiuxetan, can find cancer cells and carry cancer-killing substances to them without harming normal cells. Monoclonal antibodies, such as rituximab, can block cancer growth in different ways. Some block the ability of cancer to grow and spread. Others find cancer cells and help kill them or carry cancer-killing substances to them. Giving yttrium Y 90 ibritumomab tiuxetan with rituximab may kill more cancer cells.