We propose a standardized approach to quantitative molecular imaging (MI) in cancer patients with multiple lesions.
Methods: Twenty patients with castration-resistant prostate cancer underwent (18)F-FDG and (18)F-16β-fluoro-5-dihydrotestosterone ((18)F-FDHT) PET/CT scans. Using a 5-point confidence scale, 2 readers interpreted coregistered scan sets on a workstation. Two hundred three sites per scan (specified in a lexicon) were reviewed. (18)F-FDG-positive lesion bookmarks were propagated onto (18)F-FDHT studies and then manually accepted or rejected. Discordance-positive (18)F-FDHT lesions were similarly bookmarked. Lesional SUV(max) was recorded. Tracer- and tissue-specific background correction factors were calculated via receiver-operating-characteristic analysis of 65 scan sets.
Results: Readers agreed on more than 99% of (18)F-FDG- and (18)F-FDHT-negative sites. Positive-site agreement was 83% and 85%, respectively. Consensus-lesion maximum standardized uptake value (SUV(max)) was highly reproducible (concordance correlation coefficient > 0.98). Receiver-operating-characteristic curves yielded 4 correction factors (SUV(max) 1.8-2.6). A novel scatterplot (Larson-Fox-Gonen plot) depicted tumor burden and change in SUV(max) for response assessments.
Conclusion: Multilesion molecular imaging is optimized with a 5-step approach incorporating a confidence scale, site lexicon, semiautomated PET software, background correction, and Larson-Fox-Gonen graphing.