RecruitingDrug trialRituximab-Methotrexate-Temozolomide-Thiotepa (RMTT) Regimen As First-line Therapy for PCNS DLBCLThis study aims to observe and explore the efficacy and safety of Rituximab-Methotrexate-Temozolomide-Thiotepa (RMTT) regimen as first-line therapy for primary central nervous system diffuse large B-cell lymphomas(PCNS DLBCL)