Does CT-based lean body mass SUL is more reliable thanthose normalized by lean body mass estimated by predictive equations?

1593 Objectives: PERCIST 1.0 recommends using SUV normalized by lean body mass (SUL) as response metric. The LBM is often estimated by various predictive equations (PEs) in clinical practice. On the other hand, CT has become an established method for calculating body composition, but it requires data from the whole body, which are not typically obtained in routine PET/CT examinations. Thus, the aim of study was to introduce a novel method for estimating lean body mass (LBM) by limited field of view (FOV) CT from PET/CT examinations, and compare the results with LBM estimates of various PEs.\n Methods: A total of 233 patients who received whole-body PET/CT examinations (the arms were maintained above the head) were retrospectively retrieved. The body composition could be calculated based on threshold of CT attenuation. Two gender-based regression equations were developed using whole-body fat mass (FM) as dependent variable and the volume of trunk fat (VTF) as independent variable. Then, we can estimate whole-body LBM from trunk CT images (LBMVTF) and applied this method in a separate group of subjects (110 patients). Its results were compared with the measurement of LBM from whole-body CT (reference standard, LBMCT) and the results of 9 PEs (LBMPE1-9).\n Results: The VTF were significantly correlated with FM (r=0.981 in male and r=0.976 in female, n=233). The gender-based regression equations were developed and applied in separate group of subjects. The results showed that LBMVTF were much closer to the LBMCT than those obtained by the various PEs. The correlation analysis showed that LBMVTF correlated strongly with LBMCT for male (R2=0.986, n=110) and female (R2=0.966, n=110). These were more accurate than results from different PEs, with R2 ranging from 0.417 to 0.775 in male group (n=110) and from 0.323 to 0641 in female group (n=110). Moreover, the intra-class correlations (ICC) of this method compared with the reference standard were excellent (ICC=0.993 and 0.984 for male and female, respectively), much better than the ICC obtained with the PEs (the best ICC for PE was 0.871 for male, and 0.715 for female).\n Conclusions: LBM of the whole body could be estimated from CT data of trunk acquired in PET/CT examinations. This method could be easily implemented in practice to allow a more reliable assessment of the SUL in clinical practice notably for the therapeutic evaluations after PERCIST 1.0.