Reproducibility of 18F-FDG and 3′-Deoxy-3′-18F-Fluorothymidine PET Tumor Volume Measurements

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Abstract
The objective of this study was to establish the repeatability and reproducibility limits of several volume-related PET image–derived indices—namely tumor volume (TV), mean standardized uptake value, total glycolytic volume (TGV), and total proliferative volume (TPV)—relative to those of maximum standardized uptake value (SUVmax), commonly used in clinical practice. Methods: Fixed and adaptive thresholding, fuzzy C-means, and fuzzy locally adaptive Bayesian methodology were considered for TV delineation. Double-baseline 18F-FDG (17 lesions, 14 esophageal cancer patients) and 3′-deoxy-3′-18F-fluorothymidine (18F-FLT) (12 lesions, 9 breast cancer patients) PET scans, acquired at a mean interval of 4 d and before any treatment, were used for reproducibility evaluation. The repeatability of each method was evaluated for the same datasets and compared with manual delineation. Results: A negligible variability of less than 5% was measured for all segmentation approaches in comparison to manual delineation (5%–35%). SUVmax reproducibility levels were similar to others previously reported, with a mean percentage difference of 1.8% ± 16.7% and −0.9% ± 14.9% for the 18F-FDG and 18F-FLT lesions, respectively. The best TV, TGV, and TPV reproducibility limits ranged from −21% to 31% and −30% to 37% for 18F-FDG and 18F-FLT images, respectively, whereas the worst reproducibility limits ranged from −90% to 73% and −68% to 52%, respectively. Conclusion: The reproducibility of estimating TV, mean standardized uptake value, and derived TGV and TPV was found to vary among segmentation algorithms. Some differences between 18F-FDG and 18F-FLT scans were observed, mainly because of differences in overall image quality. The smaller reproducibility limits for volume-derived image indices were similar to those for SUVmax, suggesting that the use of appropriate delineation tools should allow the determination of tumor functional volumes in PET images in a repeatable and reproducible fashion.

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