Background: Qualitative assessment using the Deauville five-point Scale (DS) is the gold standard for interim and end-of treatment positron-emission tomography (PET) interpretation in lymphoma. In the present study we assessed the reliability and the prognostic value of different semi- quantitative parameters in comparison with DS for interim PET (iPET) interpretation in Hodgkin lymphoma (HL).
Methods: A cohort of 82 out of 260 patients with advanced stage HL enrolled in the International Validation Study (IVS), scored as 3 to 5 by the expert panel was included in the present report. Two nuclear medicine physicians blinded to patient history, clinical data and treatment outcome reviewed independently the iPET using the following parameters: DS, SUVmax, SUVpeak of the most active lesion, Qmax (ratio of SUVmax of the lesion to liver SUVmax) and Qres (ratio of SUVpeak of the lesion to liver SUVmean). The optimal sensitivity, specificity, positive and negative predictive value to predict treatment outcome was calculated for all the above parameters with the receiver operator characteristics analysis.
Results: The prognostic value of all parameters were similar, the best cut-off value being 4 for DS (area under the curve [AUC], 0.81 95% CI: 0.72-0.90), 3.81 for SUVmax (AUC 0.82 95% CI: 0.73-0.91), 3.20 for SUVpeak (AUC 0.86 95% CI: 0.77-0.94), 1.07 for Qmax (AUC 0.84 95% CI: 0.75-0.93) and 1.38 for Qres (AUC 0.84 95% CI: 0.75-0.93). The reproducibility of different parameters was similar as the inter-observer variability measured with Cohen's kappa were 0.93 (95% CI: 0.84-1.01) for the DS, 0.88 (0.77-0.98) for SUVmax, 0.82 (0.70-0.95) for SUVpeak, 0.85 (0.74-0.97) for Qres and 0.78 (0.65-0.92) for Qmax. Due to the high specificity of SUVpeak (0.87) and to the good sensitivity of DS (0.86), upon the use of both parameters the positive predictive value increased from 0.65 of the DS alone to 0.79. When both parameters were positive in iPET, 3-years Failure-Free Survival (FFS) was significantly lower compared to patients whose iPET was interpreted with qualitative parameters only (DS 4 or 5): 21% vs. 35%. On the other hand, the FFS of patients with negative results was not significantly different (88% vs. 86%).
Conclusions: In this study we demonstrated that, combining semi-quantitative parameters with SUVpeak to a pure qualitative interpretation key with DS, it is possible to increase the positive predictive value of iPET and to identify with higher precision the patients subset with a very dismal prognosis. However, these retrospective findings should be confirmed prospectively in a larger patient cohort.