Differential (18)F-FDG and (18)F-FLT Uptake on Serial PET/CT Imaging Before and During Definitive Chemoradiation for Non-Small Cell Lung Cancer.

Abstract

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 (18)F-FDG and 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT). Twenty patients with stage I-III NSCLC and candidates for radical chemoradiation therapy (60 Gy in 30 fractions over 6 wk) were recruited. (18)F-FDG and (18)F-FLT PET/CT were performed at baseline and during therapy (weeks 2 and 4). Tumor response was assessed semiquantitatively and using visual response criteria. The median and range for primary tumor volume (cm(3)) at baseline on (18)F-FDG were 28 and 2-241, respectively, and on (18)F-FLT 31 and 2-184, respectively. At week 2, (18)F-FDG was 26 (range, 2-164), and (18)F-FLT was 11 (range, 0-111). At week 4, (18)F-FDG was 19 (1-147), and (18)F-FLT was 7 (0-48). The median and range of maximum standardized uptake value (SUVmax) at baseline on (18)F-FDG were 14 and 4-31, respectively, and on (18)F-FLT 6 and 2-12, respectively. Week 2 (18)F-FDG median SUVmax was 10 (2-31), and (18)F-FLT median SUVmax was 3 (1-15); week 4 (18)F-FDG median SUVmax was 10 (2-15), and (18)F-FLT median SUVmax was 2 (2-9). There was fair agreement between visual tumor response on (18)F-FDG and (18)F-FLT during therapy (Cohen's unweighted κ statistic, 0.27 at week 2 and 0.355 at week 4). Cerebral metastases were detected on 1 baseline (18)F-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). This study demonstrates that (18)F-FLT PET/CT is a more sensitive tracer of early treatment response than (18)F-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.