Reproducibility of standardized uptake value measurements determined by 18F-FDG PET in malignant tumors

18F-FDG PET is increasingly being used to monitor the early response of malignant tumors to chemotherapy. Understanding the reproducibility of standardized uptake values (SUVs) is an important prerequisite in estimating what constitutes a significant change. METHODS: Twenty-six patients were studied on 2 separate occasions (mean interval +/- SD, 3 +/- 2 d; range, 1-5 d). A static PET/CT scan was performed 94 +/- 9 min after the intravenous injection of 383 +/- 15 MBq of 18F-FDG. Mean and maximum SUVs (SUVmean and SUVmax, respectively) were determined for regions of interest drawn around the tumor on the first study and for the same regions of interest transferred to the second study. RESULTS: SUVmean in tumors ranged from 1.49 to 17.48 and SUVmax ranged from 2.99 to 24.09. The correlation between SUVmean determined on the 2 separate visits was 0.99; the mean difference between the 2 measurements was 0.01 +/- 0.27 SUV. The 95% confidence limits for the measurements were +/-0.53. For SUVmax, the mean difference was -0.05 +/- 1.14 SUV. CONCLUSION: Our study demonstrates that repeated measurements of SUVmean performed a few days apart are highly reproducible. A decrease of 0.5 in the SUV is statistically significant.