The standardized uptake lean body mass (SUL), calculated using lean body mass (LBM), is essential for the semiquantification of (18)F-FDG uptake using PET coupled with CT to avoid a bias linked to the adipose mass. It allows the evaluation of a response to therapy according PERCIST 1.0. The aim of this study was to evaluate the reliability of a method for the estimation of the LBM using the data of the low-dose CT from PET/CT acquired over standard acquisition fields (from skull base to ischia, from vertex to ischia, from skull base to mid thigh, from vertex to mid thigh).
Methods: We wrote an automated program that determined the LBM from a CT with limited fields of acquisition and applied this method in a large (184 patients) and heterogeneous population. Its results were compared with the measurement of LBM from whole-body CT (reference standard) and the results of 5 predictive equations described in the literature.
Results: The results of LBM measurement evaluated with this technique were much closer to the reference standard than those obtained by the mathematic formulas. The intraclass correlations (ICC) of this technique compared with the reference standard were excellent (the best ICC being obtained for the largest acquisition field, from vertex to mid thigh: ICC, 0.994; 95% confidence interval [95% CI], 0.992-0.995; P < 0.0001), much better than the ICC obtained with the mathematic formulas (the best ICC for a mathematic formula was 0.841; 95% CI, 0.714-0.903; P < 0.0001). Moreover, the analysis with the Bland-Altman plot showed that the differences in mean lean masses between the studied technique and the reference standard was the smallest for the proposed technique (for the largest acquisition field, mean difference 0.2 kg with the narrowest 95% CI [-1.8 to 2.2 kg]).
Conclusion: This technique could be easily implemented on computers used in practice to allow a more reliable assessment of the SUL in clinical practice notably for the therapeutic evaluations after PERCIST 1.0.
Keywords: 18F-fluorodeoxyglucose; body fat distribution; lean body mass; positron-emission tomography; tomography; x-ray.
© 2016 by the Society of Nuclear Medicine and Molecular Imaging, Inc.