Newly diagnosed diffuse large B cell lymphoma (DLBCL) patients who enter this study will receive baseline fluorodeoxyglucose (FDG) positron emission tomography (PET) computed tomography (CT) scan at the time of initial staging. The patients will be diagnosed and undergo initial staging according to The Catholic University Lymphoma Group (CULG) Protocol.

After 1 cycle of rituximab plus cyclophosphamide, doxorubicin, vincristine, prednisone (R-CHOP) chemotherapy, early interim FDG PET/CT will be obtained after the patient recovers from nadir (usually 13 to 16 days after) following the administration of first cycle of R-CHOP,immediately before the second cycle of R-CHOP. The result of early interim FDG PET/CT study will not impact patient management, except in rare case where newly developed lesion is found and biopsy confirmed.

The same PET/CT system and analysis software will be used for all scans from baseline to surveillance for all patients enrolled in this study.

After 3 cycles of R-CHOP, a mid-therapy interim FDG PET/CT will be obtained. Patients with newly developed lesion will receive different chemotherapy regimen, while patients with stable disease, partial metabolic response or complete metabolic response will continue to receive 3 more cycles of R-CHOP.

After the completion of 6 cycles of R-CHOP, the patients will receive a FDG PET/CT scan for response assessment. Selected patients with persistent disease or very bulky tumor volume on initial staging images will receive additional radiation therapy.

The patients will be followed up every 3 months for 2 years from beginning of therapy. Physical examination and lab studies will be done usually every 3 months. Imaging studies will be performed every 3 months alternating between enhanced CT and FDG PET/CT and noted when different schedule is applied for surveillance.

The end points are changes in FDG uptake measurements between the baseline and early interim FDG PET/CT, and between baseline and mid-therapy interim FDG PET/CT scans; response assessment following completion of 6 cycles of R-CHOP with or without radiation therapy assessed by International Workshop Criteria (IWC)+PET and PET Response Criteria in Solid Tumors (PERCIST) guideline; and the 2 year disease free survival.

Inclusion Criteria:

• CD20+ diffuse large B cell lymphoma confirmed
• Therapy naïve for lymphoma
• 19 years or older
• Written informed consent

Exclusion Criteria:

• Cannot understand informed consent
• Age under 19 years old
• Previous chemotherapy or radiation therapy for lymphoma
• Known pregnancy or urine/serum hCG (+)
• Unable to lie down still on back for about 30 minutes