In diffuse large B-cell lymphoma, early assessment of treatment response by 18fluorodeoxyglucose positron emission tomography (PET) may trigger treatment modification. Reliable identification of good and poor responders is important. We compared three competing methods of interim PET evaluation.
MethodsImages from 449 patients participating in the 'Positron Emission Tomography-Guided Therapy of Aggressive Non-Hodgkin Lymphomas' trial were re-analyzed by applying the visual Deauville score and the standardized uptake value (SUV)-based qPET and SUVmax scales to interim PET scans performed after two cycles of chemotherapy.qPET relates residual lymphoma 18-fluorodeoxyglucose uptake to physiological liver uptake, converting the ordinal Deauville scale into a continuous scale and permitting a direct comparison with the continuous SUVmax scale, which is based on SUVmax changes between baseline and interim scans. Positive and negative predictive values were calculated for progression-free survival.
ResultsUsing established thresholds to distinguish between good and poor responders (visual Deauville score 1-3 vs. 4-5; SUVmax >66% vs. SUVmax ≤66%), the positive predictive value was significantly lower with Deauville thanSUVmax (38.4% versus 56.6%; p=0.03). qPET and SUVmax were strongly correlated on the log scale (Pearson's r=0.75). When plotted along corresponding percentiles, the positive predictive value curves for qPET and SUVmax were superimposable, with low values up to the 85 th percentile and a steep rise thereafter. The recommended threshold of 66% SUVmax reduction for the identification of poor responders was equivalent to qPET=2.26 corresponding to score 5 on the visual Deauville scale. The negative predictive value curves were also superimposable, but remained flat between 80% and 70%.
ConclusionsContinuous scales are better suited for interim PET-based outcome prediction than the ordinal Deauville scale. qPET and SUVmax essentially carry the same information. The proportion of poor risk patients identified is less than 15%.