[18F]FLT-PET and [18F]FDG-PET in the evaluation of radiotherapy for laryngeal cancer

SummaryThe evaluation of response to radiotherapy in patients with laryngeal cancer is a challenge because of the difficulty to differentiate between post-therapy changes and recurrent or residual tumor. Positron emission tomography is a non-invasive imaging tool that may be helpful in this differentiation. In this study, [18F]-fluoro-3′-deoxy-l-thymidine ([18F]FLT), a proliferation tracer is compared with 2-[18F]-fluoro-2-deoxy-d-glucose ([18F]FDG).Patients with primary laryngeal cancer, scheduled to undergo radiotherapy were included in this study. Patients underwent both [18F]FLT-PET and [18F]FDG-PET shortly before radiotherapy. Ten patients underwent [18F]FLT-PET and [18F]FDG-PET 2–3 months after radiotherapy. Scans were analyzed visually for areas of increased tracer uptake. The standardized uptake value (SUV) was measured as a semi-quantitative value of tracer uptake.Fourteen patients, all male, were included in this study. Both [18F]FLT-PET and [18F]FDG-PET showed increased tracer uptake in 12 out of 14 patients (86%). [18F]FDG uptake was significantly higher than [18F]FLT uptake (SUVmax: 4.5 vs. 2.4 (P = 0.002); SUVmean: 3.4 vs. 1.9 (P = 0.002)). After radiotherapy, 3 patients had histologically proven residual or recurrent laryngeal cancer. [18F]FDG was true positive in 2 out of 3 patients, whereas [18F]FLT showed increased tracer uptake in only one. Of the remaining 7 patients, [18F]FLT was true negative in all, whereas [18F]FDG showed increased uptake in one (false positive).[18F]FLT-PET is feasible in visualizing laryngeal cancer and its evaluation of treatment. The overall uptake of this tracer is significantly lower as compared with [18F]FDG, but tumor to background ratios are comparable.