Rituximab Plus Methotrexate With or Without Lenalidomide in Treating Patients With Newly Diagnosed Primary Central Nervous System Lymphoma

375mg/m2 intravenous infusion d1, every 3 weeks for 1 cycle, 6 cycles will be prescribed for induction therapy. 375mg/m2 intravenous infusion d1, every 8 weeks for 1 cycle, 4 cycles will be prescribed for maintenance therapy.

25mg orally d1-10 every 3 weeks for 1 cycle, 6 cycles will be prescribed for induction therapy. 25mg orally d1-14,d29-42 every 8 weeks for 1 cycle, 4 cycles will be prescribed for maintenance therapy.

3.5g/m2 intravenous infusion for 4 hours in d1, every 21 days for 1 cycle, 6 cycles will be prescribed.