Differential ¹⁸F-FDG and ¹⁸F-FLT uptake on serial PET/CT imaging before and during definitive chemoradiation for non-small cell lung cancer

We aimed to prospectively observe cellular metabolism and proliferation in patients with non-small-cell lung cancer (NSCLC) during radical chemoradiation therapy using serial PET/CT with 18F-FDG and 3 -deoxy-3 -18F-fluorothymidine (18F-FLT). METHODS: Twenty patients with stage I-III NSCLC and candidates for radical chemoradiation therapy (60 Gy in 30 fractions over 6 wk) were recruited. 18F-FDG and 18F-FLT PET/CT were performed at baseline and during therapy (weeks 2 and 4). Tumor response was assessed semiquantitatively and using visual response criteria. RESULTS: The median and range for primary tumor volume (cm3) at baseline on 18F-FDG were 28 and 2-241, respectively, and on 18F-FLT 31 and 2-184, respectively. At week 2, 18F-FDG was 26 (range, 2-164), and 18F-FLT was 11 (range, 0-111). At week 4, 18F-FDG was 19 (1-147), and 18F-FLT was 7 (0-48). The median and range of maximum standardized uptake value (SUVmax) at baseline on 18F-FDG were 14 and 4-31, respectively, and on 18F-FLT 6 and 2-12, respectively. Week 2 18F-FDG median SUVmax was 10 (2-31), and 18F-FLT median SUVmax was 3 (1-15); week 4 18F-FDG median SUVmax was 10 (2-15), and 18F-FLT median SUVmax was 2 (2-9). There was fair agreement between visual tumor response on 18F-FDG and 18F-FLT during therapy (Cohen s unweighted kappa statistic, 0.27 at week 2 and 0.355 at week 4). Cerebral metastases were detected on 1 baseline 18F-FLT scan, resulting in palliative management. Progressive disease was detected on week 2 scans in 3 patients, resulting in changes to radiation therapy (2 patients) and treatment intent (1 patient). CONCLUSION: This study demonstrates that 18F-FLT PET/CT is a more sensitive tracer of early treatment response than 18F-FDG PET/CT. The ability of these tracers to detect distinct biologic processes may lead to their use as biomarkers for personalized radiation therapy and prognosis in the future.