| Summary: | <h4>Purpose</h4>The study objective was to compare the prognostic value of interim and end-of-treatment FDG PET/CT using five therapeutic evaluation criteria in patients with diffuse large B cell lymphoma (DLBCL).<h4>Methods</h4>181 patients were retrospectively analysed. All patients underwent FDG-PET at baseline and after four cycles (iPET4) of first-line chemotherapy and 165 at the end-of-treatment (PET-eot). Ratio Deauville score (rDS) (SUVmax-target residual lesion/SUVmax-liver) was measured in iPET4 and PET-eot, and its optimal threshold was determined using receiver operating characteristic (ROC) curve analysis. Deauville score (DS) (iPET4 and PET-eot), ΔSUVmax, ΔSUVmax determined according to Menton 2011 criteria (ΔSUVmax+DS) and ΔSUVmax+rDS were also evaluated (iPET4 only). Median follow-up was 44 months.<h4>Results</h4>ROC analysis revealed the optimal cut-off value was 1.4-fold of SUVmax-liver on iPET4 and PET-eot. On iPET4, positive predictive value (PPV) of rDS was significantly better than DS: 81.58% vs. 67.79%. In univariate analysis, the five interpretation methods were statistically significant (p<0.0001 for progression-free survival [PFS] and overall survival [OS]). In multivariate analysis, only rDS was an independent prognostic factor (p = 0.0002 and p<0.0001 for PFS and OS, respectively). On PET-eot, similarly, the two therapeutic evaluation criteria analysed (rDS and DS) were statistically significant at the univariate level (p<0.0001). rDS was the only significant prognostic factor in multivariate analysis (p<0.0001). PPV and accuracy of rDS were also better than DS.<h4>Conclusions</h4>rDS with a tumor/liver ratio of 1.4 is a robust prognostic factor in patients with DLBCL on iPET4 and PET-eot.
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