18F-FLT PET/CT imaging is incompetent to perform pretreatment evaluation in advanced gastric cancer: Comparison with 18F-FDG PET/CT imaging

Objectives The aim was to evaluate the ability of 18F-FLT PET/CT imaging to detect both primary tumors and common metastases in advanced gastric cancer, in comparison with 18F-FDG PET/CT imaging, thus to assess its capacity to perform pretreatment evaluation in advanced gastric cancer.

Methods 48 patients with pathologically proven locally advanced gastric cancer were enrolled. 7/48 were postoperative patients without remnant stomach or anastomotic recurrence diagnosed by gastroscopy. Attenuation-corrected whole body 18F-FLT and 18F-FDG PET/CT (low dose CT) imaging were performed in two consecutive days before chemotherapy.

Results Focal activity accumulations were visible in primary tumors in 38/41 on 18F-FLT and 39/41 on 18F-FDG PET/CT respectively, with the sensitivities of 92.7% vs. 95.1%. 3/38 quite easily went neglected on 18F-FLT for almost been covered by the hepatic high background uptake. Because of the high 18F-FLT physiologic uptake in liver (median SUVmax 5.5, range 4.5~8.3) and bone marrow (median SUVmax 14.8, range 10.8~22.0), the sensitivities of detecting liver metastases and bone metastases for 18F-FLT and 18F-FDG PET/CT were 27.3% (6/22) vs. 100% (22/22) and 1/7 (14.3%) vs. 7/7 (100%) respectively, P<0.05. Metabolically positive findings of lymph nodes, peritoneal and ovarian metastases were similar between the two modalities, they were 97.4% (38/39) vs. 94.9% (37/39), 87.5% (21/24) vs. 91.7% (22/24) and 90.9% (10/11) vs. 90.9% (10/11) for 18F-FLT vs. 18F-FDG respectively, P>0.05.

Conclusions 18F-FLT PET/CT imaging was not recommended to perform pretreatment assessment in advanced gastric cancer for it was incompetent to evaluate liver and bone metastases, and the hepatic high background uptake may cover the gastric primary tumors which located adjacent to liver.