Repeatability of ¹⁸F-FDG PET/CT in Advanced Non–Small Cell Lung Cancer: Prospective Assessment in 2 Multicenter Trials

Abstract

PET/CT with the glucose analog ¹⁸F-FDG has several potential applications for monitoring tumor response to therapy in patients with non–small cell lung cancer (NSCLC). A prerequisite for many of these applications is detailed knowledge of the repeatability of quantitative parameters derived from ¹⁸F-FDG PET/CT studies. Methods: The repeatability of the ¹⁸F-FDG signal was evaluated in 2 prospective multicenter trials. Patients with advanced NSCLC (tumor stage III–IV) underwent two ¹⁸F-FDG PET/CT studies while not receiving therapy. Tumor ¹⁸F-FDG uptake was quantified by measurement of the maximum standardized uptake value within a lesion (SUV_max) and the average SUV within a small volume of interest around the site of maximum uptake (SUV_peak). Analysis was performed for the lesion in the chest with the highest ¹⁸F-FDG uptake and a size of at least 2 cm (target lesion) as well as for up to 6 additional lesions per patient. Repeatability was assessed by Bland–Altman plots and calculation of 95% repeatability coefficients (RCs) of the log-transformed SUV differences. Results: Test–retest repeatability was assessed in 74 patients (34 from the ACRIN 6678 trial and 40 from the Merck MK-0646-008 trial). SUV_peak was 11.57 ± 7.89 g/mL for the ACRIN trial and 6.89 ± 3.02 for the Merck trial. The lower and upper RCs were −28% (95% confidence interval [CI], −35% to −23%) and +39% (95% CI, 31% to 54%) in the ACRIN trial, indicating that a decrease of SUV_peak by more than 28% or an increase by more than 39% has a probability of less than 2.5%. The corresponding RCs from the Merck trial were −35% (95% CI, −42% to −29%) and +53% (95% CI, 41% to 72%). Repeatability was similar for SUV_max of the target lesion, averaged SUV_max, and averaged SUV_peak of up to 6 lesions per patient. Conclusion: The variability of repeated measurements of tumor ¹⁸F-FDG uptake in patients with NSCLC is somewhat larger than previously reported in smaller single-center studies but comparable to that of gastrointestinal malignancies in a previous multicenter trial. The variability of measurements supports the definitions of tumor response according to PET Response Criteria in Solid Tumors.