Practical Approach for Comparative Analysis of Multilesion Molecular Imaging Using a Semiautomated Program for PET/CT

Abstract

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 ¹⁸F-FDG and ¹⁸F-16β-fluoro-5-dihydrotestosterone (¹⁸F-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. ¹⁸F-FDG–positive lesion bookmarks were propagated onto ¹⁸F-FDHT studies and then manually accepted or rejected. Discordance-positive ¹⁸F-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 ¹⁸F-FDG– and ¹⁸F-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.