Study on Predicting Response to Standard First-Line Treatment in Diffuse Large B-Cell Lymphoma (DLBCL) Patients Using ctDNA Combined With PET

Inclusion Criteria: * Age ≥ 18 years old. * Previously untreated CD20-positive DLBCL patients, including the following types according to the 2016 WHO classification of lymphoid neoplasms: DLBCL, not otherwise specified (NOS) including germinal center B-cell type and activated B-cell type; T-cell/histiocyte-rich large B-cell lymphoma; Epstein - Barr virus-positive DLBCL, NOS; ALK-positive large B-cell lymphoma; HHV8-positive DLBCL, NOS; high-grade B-cell lymphoma with MYC and BCL2 and/or BCL6 rearrangements (double-hit or triple-hit lymphoma); high-grade B-cell lymphoma, NOS. * Signed informed consent form (ICF). * Eastern Cooperative Oncology Group (ECOG) performance status score 0 - 2, with an expected survival greater than 12 months. * Have at least one measurable two-dimensional lesion determined by clinical examination, CT scan, or MRI: ① lymph nodes \> 1.5 cm; ② other non-lymph node lesions ≥ 1.0 cm. * Good function of major organs: Hematological function: absolute neutrophil count ≥ 1,000/mm³, platelet count ≥ 75,000/mm³; Liver function: ALT/AST \< 3 times the upper limit of normal (ULN) and total bilirubin ≤ 1.5× ULN (for patients with Gilbert syndrome, hilar compressive adenopathy-induced cholestasis, liver involvement or lymphoma-induced biliary obstruction \< 5 times ULN); Renal function: creatinine clearance \> 30 mL/min, creatinine ≤ 1.5× ULN; Pulmonary function: indoor oxygen saturation ≥ 95%; Cardiac function: no obvious cardiac insufficiency or cardiovascular disease. * Fertile patients must be willing to take highly effective contraceptive measures during the study and within 120 days after the last administration of treatment. Exclusion Criteria: * Patients planned to receive short-cycle chemotherapy and radiotherapy. * Subjects judged by the investigator to have any factors affecting compliance with the protocol, including uncontrollable medical, psychological, family, sociological or geographical conditions; or unwilling or unable to comply with the procedures required in the study protocol. * Known human immunodeficiency virus (HIV) infection or positive immunassay. * Viral infections that cannot be controlled by antiviral drugs, such as herpesvirus active infection, acute or chronic active hepatitis B, acute or chronic active hepatitis C, etc. (Note: Chronic HBV carriers or inactive HBsAg-positive subjects with HBV-DNA below the detection limit can be enrolled, requiring clinical evaluation, and if appropriate, preventive antiviral treatment is required; HCV antibody-negative subjects can be enrolled, and HCV antibody-positive patients need to be tested for HCV-RNA, and if negative, they can be enrolled). * Patients with uncontrolled lymphoma central nervous system infiltration (central nervous system diseases diagnosed at the initial diagnosis are allowed, provided that complete remission of central nervous system diseases is achieved and maintained and there is no central nervous system disease at recurrence). * Pregnant or lactating patients. * Other concurrent serious diseases or medical conditions that would interfere with participation in the study.