The effect of new formulas for lean body mass on lean- body-mass-normalized SUV in oncologic 18F-FDG PET/CT

Due to better precision and intercompatibility, the use of lean body mass (LBM) as mass estimate in the calculation of standardized uptake values (SUV) has become more common in research and clinical studies today. Thus, the equations deciding this quantity have to be verified in order to choose the ones that best represents the actual body composition. Methods - LBM was calculated for 44 patients examined with 18F-FDG PET/CT scans by means of James’ and Janmahasatians’ sex specific predictive equations and the results validated using a CT based method. The latter method makes use of the eyes-to-thighs CT from the PET/CT aquisition protocol and segments the voxels according to Hounsfield Units. Intraclass correlation coefficients (ICC) and Bland-Altman plots have been used to assess agreement between the various methods. Results - A mean difference of 6.3kg (-15.1 kg to 2.5 kg LOA) between LBMjames and LBMCT1 was found. This is higher than the observed mean difference of 3.8kg (-12.5 kg to 4.9 kg LOA) between LBMjan and LBMCT1. In addition, LBMjan had higher ICC with LBMCT1 of rI = 0.87 (rL = 0.60, rU = 0.94) than LBMjames with rI = 0.77 (rL = 0.11, rU = 0.91). Thus, we obtained better agreement between and LBMjan and LBMCT1. Although there were exceptions, the overall effect on SUL values was that SULjames values were greater than SULjan values. Conclusion - From our results, we have verified the reliability of the LBMjan suggested formulas with a CT derived reference standard. Compared with the more traditional and available set of equations LBMjames, the LBMjan formulas tend to yield better agreement