Inclusion Criteria:  age ≥ 18 years with high CNS risk, which was defined as involvement of more than one extranodal site, or involvement of particular extranodal sites such as bone marrow, breasts, testes, paranasal sinuses, epidural space, adrenal glands, kidney and female genital system; first-line treatment planned to be RCHOP absence of CNS involvement at presentation  Exclusion Criteria:  primary CNS lymphoma already have CNS involvement at diagnosis primary mediastinal lymphoma, intravascular large B-cell lymphoma, DLBCL leg-type, Burkitt lymphoma, high-grade lymphomas, double expressor lymphoma with active infection or other malignancy severe liver or kidney insufficiency allergy to any medication we plan to use