Volume-based parameters on FDG PET may predict the proliferative potential of soft-tissue sarcomas.

INTRODUCTION: Soft-tissue sarcomas (STS) are rare types of tumors that have variable levels of tumor differentiation. F-18 fluorodeoxyglucose positron emission tomography (FDG PET) has been established as an useful tool for STS patients, and the metabolic tumor volume (MTV) and total lesion glycolysis (TLG) are reported to be useful in various cancers. We compared the diagnostic value of four PET parameters (maximum standardized uptake value [SUVmax], SUVmean, MTV, and TLG) from two acquisition timings for predicting the expression of the pathological marker of cell proliferation Ki-67, based on pathological investigation. MATERIALS AND METHODS: In this retrospective study, we investigated 20 patients (59 ± 19 years old, 18-87 years old) with pathologically confirmed STS who underwent FDG PET before surgical intervention. The patients fasted ≥ 6 h before the intravenous injection of FDG. The whole body was scanned twice; at an early phase (61.5 ± 2.6 min) and at a delayed phase (118.0 ± 2.1 min) post-injection. The SUVmax, SUVmean, MTV, and TLG of the primary lesion were measured with a tumor boundary determined by SUV ≥ 2.0. Ki-67 was measured using MIB-1 immunohistochemistry. We used Pearson's correlation coefficient to analyze the relationships between the PET parameters and Ki-67 expressions. The Kaplan-Meier analysis with the log-rank test was performed to compare overall survival between high-group and low-group at each of the four PET parameters and Ki-67 expression. RESULTS: All four PET parameters at each phase showed significant correlations with Ki-67. Among them, the Pearson's correlation coefficient (r) was largest for TLG (r = 0.76 and 0.77 at the early and delayed phases, respectively), followed by MTV (0.70 and 0.72), SUVmax (r = 0.65 and 0.66), and SUVmean (r = 0.62 and r = 0.64). From early to delayed phases, the SUVmax and SUVmean both increased in all 20 patients, whereas the MTV and TLG increased in 13/20 (65%) and 16/20 (80%) patients, respectively. None of the %increases of the PET parameters were significantly correlated with Ki-67. The overall survival was shorter for high-SUVmax, high-SUVmean, high-TLG, and high-Ki-67 groups than the other groups, although the difference did not reach statistical significance. CONCLUSION: The SUVmax, SUVmean, MTV, and TLG acquired at both 1 and 2 h after injection showed significant correlations with Ki-67. Among them, correlation coefficient with Ki-67 expression was highest for TLG, although the best parameter should be determined in a larger population. The delayed-phase FDG PET was equally useful as that of early-phase to predict tumor aggressiveness in STS.

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 (MTVp and TLGp; p = 2.0, 2.5, 3.0, 3.5), (2) the fixed% SUVmax threshold method (MTVq% and TLGq%; q = 35, 40, 45), and (3) the adaptive region-growing method (MTVARG and TLGARG). 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). MTV3.0 and MTV3.5 resulted in a significant increase from the early to delayed phase (P < 0.05 for both), whereas MTV2.0 and MTV2.5 neither increased nor decreased (P = n.s.). All of the MTVq% values significantly decreased over time (P < 0.01), whereas MTVARG 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. MTV2.0 and MTV2.5 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.