OBJECTIVETo investigate the prognosis value of early and interim ¹⁸F-FDG-PET/CT scan in patients with diffuse large B- cell lymphoma （DLBCL） to establish the suitable criteria for evaluating posttherapeutic lesions in scans.

METHODSFifty- six newly diagnosed DLBCL patients were enrolled in the study, and underwent baseline, early and interim ¹⁸F- FDG PET/CT scans. Five- point and % ΔSUVmax criteria were used separately to interpret ¹⁸F- FDG PET/CT images. Interobserver reproducibility was assessed with the kappa test（κ）, and thresholds of %ΔSUVmax were calculated via receiver operating characteristic curve（ROC）. Survival curves were obtained using Kaplan-Meier curves and log-rank test. Cox regression analysis was used for multi-factor analysis.

RESULTSMedian follow-up was 24 months（6 to 42 months）. The kappa value of the five- point scale was above 0.600 with the reference background set in the liver（Score≥4）. The optimal threshold of %ΔSUVmax was 81% for early PET/CT and 74% for interim PET/CT. Survival analysis showed both early and interim PET/CT scans could predict the outcome of 56 patients with DLBCL, and 3-year PFS and OS of PET-negative patients were significantly higher than those of PET-positive ones（P<0.05）. Five-score criteria were more accurate in evaluating 3- year PFS of DLBCL patients in the interim PET/CT scan（76.79%）. %ΔSUVmax criteria were better for interpreting 3-year OS（76.79% and 83.93%）. Multi-factor analysis demonstrated that early and interim PET/CT were solid predicting factors for DLBCL patients.

CONCLUSIONEarly and interim PET/CT scans could predict the outcome of patients with DLBCL, treated with R-CHOP/CHOP. Three-year OS was more accurate in early and interim PET/CT using 66 %ΔSUVmax criteria as an interpretation, while 3-year PFS was more accurate in interim PET/CT by five scores criteria.