Imaging gastric cancer with PET and the radiotracers 18F-FLT and 18F-FDG:: A comparative analysis

In this pilot study, we evaluated 3'-deoxy-T-F-18-fluorothymidine (FLT) PET for the detection of gastric cancer and compared the diagnostic accuracy with that of F-18-FDG PET. Methods: Forty-five patients (31 male and 14 female) with histologically proven locally advanced gastric cancer underwent attenuation-corrected whole-body F-18-FLT PET and F-18-FDG PET/CT (low-dose CT). F-18-FLT emission images were acquired on a full-ring PET scanner 45 min after the injection of 270-340 MBq of F-18-FLT. F-18-FDG PET/CT was performed 60 min after the injection of 300-370 MBq of F-18-FDG. Mean standardized uptake values for F-18-FLT and F-18-FDG were calculated using circular ROIs (diameter, 1.5 cm) in the primary tumor manifestation site, in a reference segment of the liver, and in the bone marrow and were compared on a lesion-by-lesion basis. Results: According to the Lauren classification, 15 tumors (33%) were of the intestinal subtype and 30 (67%) of the nonintestinal subtype. F-18-FLT PET images showed high contrast for the primary tumor and proliferating bone marrow. In all patients (45/45), focal F-18-FLT uptake could be detected in the primary tumor. In contrast, 14 primary tumors were negative for F-18-FDG uptake, with lesional (18)FFDG uptake lower than or similar to background activity. The mean standardized uptake value for F-18-FLT in malignant primaries was 6.0 +/- 2.5 (range, 2.4-12.7). In the subgroup of F-18-FDG-positive patients, the mean value for F-18-FDG was 8.4 +/- 4.1 (range, 3.8/19.0), versus 6.8 +/- 2.6 for F-18-FLT (Wilcoxon test: P = 0.03). Comparison of mean F-18-FLT and F-18-FDG uptake in tumors with signet ring cells revealed no statistically significant difference between the tracers (6.2 +/- 2.1 for F-18-FLT vs. 6.4 +/- 2.8 for F-18-FDG; Wilcoxon test: P = 0.94). Conclusion: The results of this study indicate that imaging gastric cancer with the proliferation marker F-18-FLT is feasible. F-18-FLT PET was more sensitive than F-18-FDG PET, especially in tumors frequently presenting without or with low F-18-FDG uptake, and may improve early evaluation of response to neoadjuvant treatment.