Does quantitative SUV-based analysis improve reproducibility of interpretation of posttherapy PET-CT scans in Hodgkin's and aggressive non-Hodgkin's lymphoma?

Objectives International Harmonization Project (IHP)-based interpretation of post-therapy (post-Rx) lymphoma PET/CT is now widely used but there is little data regarding its reproducibility. We determined interobserver variability in interpretation of post-Rx PET/CTs performed at 90 minutes post FDG injection in pts with lymphoma. These interpretation criteria were compared with 3 quantitative approaches to determine whether these improve reproducibility and accuracy of scan interpretation.

Methods 3 expert nuclear medicine MDs blinded to pt outcome independently visually interpreted post-therapy PET/CTs based on the IHP-criteria. 3 quantitative approaches were used: RM SUVmax, RM SUVmax to mediastinal blood pool SUVmean (RMmx:MBPmn) ratio and RM SUVmax to liver SUVmean ratio RMmx:Liver mn). Positive predictive value (PPV), negative predictive value (NPV) and accuracy for prediction of residual disease/progression were compared between the two approaches.

Results Of the 50 patients studied, 30 pts had 60 RMs seen. When interpreted visually by the 3 readers, scan agreement (positive/negative) was noted in 82% the 60 RMs. PPV, NPV, and accuracy of RM interpretation for the 3 readers were 67%, 79% and 81%; 100%, 100%, and 100%; 82%, 90%, 92%, respectively. In contrast, cut-off RM SUVmax and RMmx:MBP mn ratio of 2.5 and 1.75, respectively in PPV, NPV and accuracy of 92%, 100% and 97% with areas under the ROC curve of 0.993, 0.999, and 1.0 for the RMmx, RMmx/MBP mn and RMmx/Liver mn. PET/CTs of the 20 patients without RMs were called negative by all 3 readers.

Conclusions Visual IHP-criteria provide fairly reproducible interpretations among nuclear medicine MDs but with only moderate PPV and accuracy. Quantitative approaches provide substantial improvement in PPV and accuracy upon the IHP criteria. As these approaches are potentially more reproducible, they should be considered for more consistent interpretation