Response Assessment Using 18F-FDG PET Early in the Course of Radiotherapy Correlates with Survival in Advanced-Stage Non–Small Cell Lung Cancer

Abstract

This study investigated the possibility of early response assessment based on (18)F-FDG uptake during radiotherapy with respect to overall survival in patients with non-small cell lung cancer. (18)F-FDG PET/CT was performed before radiotherapy and was repeated in the second week of radiotherapy for 34 consecutive lung cancer patients. The CT volume and standardized uptake value (SUV) parameters of the primary tumor were quantified at both time points. Changes in volume and SUV parameters correlated with 2-y overall survival. The average change in mean SUV in the primary tumor of patients with a 2-y survival was a decrease by 20% ± 21%-significantly different (P < 0.007) from nonsurvivors, who had an increase by 2% ± 22%. A sensitivity and specificity of 63% and 93%, respectively, to separate the 2 groups was reached for a decrease in mean SUV of 15%. Survival curves were significantly different using this cutoff (P = 0.001). The hazard ratio for a 1% decrease in mean SUV was 1.032 (95% confidence interval, 1.010-1.055). Changes in tumor volume defined on CT did not correlate with overall survival. The use of repeated (18)F-FDG PET to assess treatment response early during radiotherapy is possible in patients undergoing radiotherapy or sequential or concurrent chemoradiotherapy. A decrease in (18)F-FDG uptake by the primary tumor correlates with higher long-term overall survival.