Abstract
BackgroundThe standardized uptake value (SUV) is the nearly exclusive means for quantitative evaluation of clinical [18F-]fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) whole body investigations. However, the SUV methodology has well-known shortcomings. In this context, it has been recognized that at least part of the problems can be eliminated if tumor SUV is normalized to the SUV of a reference region in the liver (tumor-to-liver [TLR] ratio). In recent publications, we have systematically investigated the tumor-to-blood SUV ratio (SUR) for normalization of tumor SUVs which in our view offers principal advantages in comparison to TLR. The aim of this study was a comprehensive comparison of TLR and SUR in terms of quantification of tumor lesions.Methods18F-FDG PET/CT was performed in 424 patients (557 scans) with different tumor entities prior to radio(chemo)therapy. In the PET images, SUVmax of the primary tumor was determined. SUVliver was calculated in the inferior right lobe of the liver. SUVblood was determined by manually delineating the aorta in the low-dose CT. TLR and SUR were computed and scan time corrected to 60 min p.i. (TLRtc and SURtc). Correlation analysis was performed for SUVliver vs. SUVblood, TLR vs. SUR, SUVliver/SUVblood vs. SUVblood,SURtc/TLR vs. SURtc, and SURtc/TLRtc vs. SURtc. Variability of the respective ratios was assessed via histogram analysis. The prognostic value of TLR and TLRtc for distant metastases-free survival (DM) was investigated with univariate Cox regression in a homogeneous subgroup (N = 130) and compared to previously published results for SUV and SURtc.ResultsCorrelation analysis revealed a linear correlation of SUVliver vs. SUVblood (R 2=0.83) and of TLR vs. SURtc (R2=0.92). The SUVliver/SUVblood ratio (mean ± s.d.) was 1.47 ± 0.18. For the SURtc/TLR ratio, we obtained 1.14 ± 0.21 and for the SURtc/TLRtc ratio 1.38 ± 0.17. Survival analysis revealed TLR and TLRtc as significant prognostic factors for DM (hazard ratio [HR] = 3.3 and HR = 3, respectively). Both hazard ratios are lower than that of SURtc (HR = 4.1) although this reduction does not reach statistical significance for the given limited group size. HRs of TLR and SURtc are both significantly higher than HR of SUV (HR = 2.2).ConclusionsSuitability of the liver as surrogate of arterial tracer supply for SUV normalization via TLR computation is limited. Further studies in sufficiently large patient groups are required to better characterize the relative performance of SUV, TLR, and SUR in different settings.
Highlights
The standardized uptake value (SUV) is the nearly exclusive means for quantitative evaluation of clinical [18F-]fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) whole body investigations
We investigate the prognostic value of TLR and TLRtc for distant metastases-free survival (DM) using univariate Cox regression
The mean intra-individual paired differences, SUVblood and SUVliver, in 84 patients receiving two PET scans on different days were 0.05 ± 0.32 and 0.24 ± 0.42, respectively. This demonstrates that the interand intra-subject variability of both SUVs are of very similar magnitude
Summary
The standardized uptake value (SUV) is the nearly exclusive means for quantitative evaluation of clinical [18F-]fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) whole body investigations. In this context, it has been recognized that at least part of the problems can be eliminated if tumor SUV is normalized to the SUV of a reference region in the liver (tumor-to-liver [TLR] ratio ). [1,2,3,4,5,6] all of which adversely affect the reliability of the SUV as a surrogate of the metabolic rate of FDG (and of glucose consumption) In this context, it has been recognized repeatedly that at least part of the mentioned problems can be reduced or eliminated if tumor SUV is normalized to the SUV of a suitable reference region [7]. Using the tumor-to-liver-ratio (TLR) obviously removes some of the SUV limitations, i.e. possible inaccuracies regarding injected dose, scanner calibration, and patient weight index (either actual body weight, lean body mass [14], or body surface area [15])
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