151751-Najiba-Chargi

183 Systemic therapy: skeletal muscle mass and chemoradiotherapy MRI was previously found to be excellent (ICC 0.97, p<0.01) 15 , skeletal muscle area measure- ments by CT and MRI were analyzed together. The skeletal muscle area was calculated as the sum of the delineated areas of the paravertebral muscles and both sternocleidomastoideus muscles. SMM is often used interchangeably with LBM, however LBM includes SMM, as well as bones and bodily fluids. Therefore, we also predicted LBM using Mourtzakis formula where the LBM in kilograms by use of the skeletal muscle area obtained by cross-sectional imaging was used. 16 Mourtzakis formula is based on skeletal muscle area measured at the third lumbar vertebrae (L3), not C3. Therefore, skeletal muscle area at the level of C3 was first converted to skeletal muscle area at the level of L3 using a previously published formula. 17 Absolute SMM is strongly correlated with height, therefore SMM must be calculated as an index of relative SMM. 18 This is the same to the use of body mass index (body weight (kg)/height 2 (m 2 )) for clas - sifying relative adiposity. Skeletal muscle area at L3 is normalized to stature (using squared height similar to calculating BMI) to obtain the lumbar skeletal muscle mass index (LSMI). The LSMI cut-off value used in this study was a LSMI of 43.2 cm 2 /m 2 , as previous established in a separate cohort of LA-HNC patients. 8 This cut-off value was used to categorize patients into patients with low SMM and patients without low SMM. Thus, in further analysis low SMM was defined as LSMI ≤43.2 cm 2 /m 2 . DOSE-LIMITING TOXICITY We defined cisplatin DLT as any toxicity resulting in a cisplatin dose-reduction of ≥ 50%, a treatment delay of ≥ 4 days or a termination of cisplatin-based chemotherapy after the first or second cycle of therapy. STATISTICAL ANALYSIS Data analysis was performed using IBM SPSS statistics 25. Demographic, clinical, biochem - ical and anthropometric data were reported for the total group and according to SMM and DLT status. Baseline measures for these groups were described using descriptive statistics. Normally distributed variables were shown as means ± standard deviation (SD), non-normally distributed variables were shown as medians with an interquartile range (IQR). Normality was investigated using the Kolmogorov-Smirnov test. Categorical variables were described as frequencies with corresponding percentages. Chi-square statistics were used for analyzing differences between the frequencies of each categorical variable with the presence or absence of low SMM and DLT. Wald logistic regression analysis was used for univariate andmultivariate analysis of the predictors for cisplatin DLT. Covariates used in the multivariate analysis were selected based on statistical significance in univariate analysis or on clinical relevance. Statis - tical significance was evaluated at the 0.05 level using 2-tailed tests. The Hosmer-Lemeshow test was performed to test the goodness-of-fit of the multivariate analysis model. 10