151751-Najiba-Chargi

277 Systemic therapy: skeletal muscle mass changes and chemoradiotherapy measuring CSA at the level of C3. The SMA was calculated as the sum of the delineated areas of the paravertebral muscles and both sternocleidomastoid muscles. When measurement of SMA of one sternocleidomastoid was not possible, due to e.g., lymph node invasion or radical neck dissection, we calculated the SMA of the other sternocleidomastoid and multiplied this by two. SMA at the level of C3 was first converted to SMA at the level of L3 using a previously published formula. 25 The SMA at the level of L3 was corrected for patients’ squared height to obtain the lumbar skeletal muscle mass index (LSMI). The LSMI cut-off value for the diagnosis of low SMM chosen in this study was a LSMI of 43.2 cm 2 /m 2 , as previous calculated in a separate cohort of LA-HNC patients. 12 This cut-off value was used to categorize patients into patients with low SMM and patients without low SMM. Thus, in further analyses low SMM was defined as LSMI ≤ 43.2 cm 2 /m 2 . SKELETAL MUSCLE MASS CHANGES Relative changes of SMM were calculated by using the following formula: Relative change of SMM = (SMA after CRT – SMA before CRT) / (SMA before CRT) x 100%. Hereafter, the standard deviation (SD) of the relative changes in SMM were calculated as pre - viously described by Brown et al. 26 in order to derive five categories of changes in SMM in the 5 th to 95 th percentiles: Stable changes in SMM: no change ± 1 SD from baseline Moderate gain in SMM: ≥ 1SD to < 2 SD of gain from baseline Moderate loss in SMM: ≥ 1SD to <2 SD of loss from baseline Large gain in SMM: ≥2 SD from baseline Large loss in SMM: ≥2 SD from baseline SURVIVAL OS was defined as the time between the date of histologic diagnosis of LA-HNC and death, or date of last follow-up. DFS was defined as the time between the date of histologic diagnosis of LA-HNC and the date of pathologic confirmed recurrence or date of last follow-up, whichever occurred first. STATISTICAL ANALYSIS Data analysis was performed using IBM SPSS statistics 25. Demographic and clinical data were reported for the included patients. Baseline measures for these groups were described using descriptive statistics. Normally distributed variables were shown as means ± standard devi - ation (SD), non-normally distributed variables were shown as medians with an interquartile range (IQR). Normality was investigated using the Kolmogorov-Smirnov test. Independent sample student’s t -tests were used to compare the means of normally distributed continuous variables with regard to presence or absence of low SMM. Categorical variables were described 15