151751-Najiba-Chargi

47 Diagnostics: measuring skeletal muscle mass on CT and MRI Segmentation of muscle tissue on CT and MRI was manually performed using the Volumetool v.1.6.5 research software package 18 by a single researcher (N.C). The researcher was blinded to the outcome since all CSA values were retrieved at the end of the study. The axial imaging slide which showed both the transverse processes and the entire vertebral arch was selected for segmentation of muscle tissue. For CT imaging, muscle area was defined as the pixel area between the radiodensity range of -29 and +150 Hounsfield Units (HU), which is specific for muscle tissue. For MRI, muscle area was manually segmented, and fatty tissue was manually excluded. The CSA was calculated as the sum of the delineated areas of the paravertebral muscles and both sternocleidomastoid muscles. CSA at the level of C3 measured by CT and MRI was used for variability analysis. Data analysis was performed using IBMSPSS statistics 25. Variability between CT andMRI in CSAmeasurements of SMMwas determined by the intraclass correlation coefficient (ICC) which is based on analysis of variance. 19 The ICC was calculated using a two-way mixed-effects model with absolute agreement. An ICC of 1 represents no variance in CSA assessment of SMM by CT and MRI. Bland and Altman method were used to calculate the mean difference and to evaluate the 95% limits of agreements between CSA measurements of SM by CT and MRI. 20 In total, 50 OPSCC patients were included. Demographic and clinical data are presented in table 1. Low SMMwas identified by MRI in 30 (60%) patients and by CT in 31 (62%) patients. The overall ICC for the CSAmeasurements of SMM obtained by CT and MRI was excellent (0.97; 95% CI 0.94 - 0.98, p < 0.01). Figure 1 shows the scatter plot of the correlation between CSA mea - surements by CT and MRI. As shown in this figure, there is a positive linear and a statistically significantly strong (r 2  = 0.94, p<0.01) relationship. Figure 2 shows the Bland and Altman plot with the corresponding 95% limits of agreements; the mean difference of CSA measurements between CT and MRI was less than 1 cm 2 (mean difference 0.87 cm 2 ; 95% CI -5.24 - 6.98). Table 1. Demographic and clinical characteristics of included patients Variables N % Human papillomavirus status Positive Negative Unknown 18 21 11 36 42 22 Gender Female Male 14 36 28 72 Age (years) (M, SD) 61.3 9.4 Body mass index (kg/m 2 ) <20 kg/m 2 20-24.9 kg/m 2 25-29.9 kg/m 2 ≥30 kg/m 2 9 24 8 9 18 48 16 18 3