Reproducibility and uptake time dependency of volume-based parameters on FDG-PET for lung cancer

BACKGROUND: Volume-based parameters, such as metabolic tumor volume (MTV) and total lesion glycolysis (TLG), on F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) are useful for predicting treatment response in nonsmall cell lung cancer (NSCLC). We aimed to examine intra- and inter-operator reproducibility to measure the MTV and TLG, and to estimate their dependency on the uptake time. METHODS: Fifty NSCLC patients underwent preoperative FDG-PET. After an injection of FDG, the whole body was scanned twice: at the early phase (61.4 ± 2.8 min) and delayed phase (117.7 ± 1.6 min). Two operators independently defined the tumor boundary using three different delineation methods: (1) the absolute SUV threshold method (MTV(p) and TLG(p); p = 2.0, 2.5, 3.0, 3.5), (2) the fixed% SUVmax threshold method (MTV(q%) and TLG(q%); q = 35, 40, 45), and (3) the adaptive region-growing method (MTV(ARG) and TLG(ARG)). Parameters were compared between operators and between phases. RESULTS: Both the intra- and inter-operator reproducibility were high for all parameters using any method (intra-class correlation > 0.99 each). MTV(3.0) and MTV(3.5) resulted in a significant increase from the early to delayed phase (P < 0.05 for both), whereas MTV(2.0) and MTV(2.5) neither increased nor decreased (P = n.s.). All of the MTV(q%) values significantly decreased over time (P < 0.01), whereas MTV(ARG) and TLG with any delineation method increased significantly (P < 0.05). CONCLUSIONS: High reproducibility of MTV and TLG was obtained by all of the methods used. MTV(2.0) and MTV(2.5) were the least sensitive to uptake time, and may be good alternatives when we compare images acquired with different uptake times, although applying constant uptake time is important for volume measurement.