151751-Najiba-Chargi

297 Systemic therapy: skeletal muscle mass and oropharyngeal carcinoma whereas HPV-positive patients with more than 10 pack-years and a N2b-N3 nodal stage and HPV-negative patients with less than 10 pack-years and a T1-3 tumor stage were considered to be at a intermediate risk, HPV-negative patients with more than 10 pack-years or with less than 10 pack-years but a T4 tumor stage were considered to be at high risk. 9 Overall survival (OS) was defined as the time between the date of histologic diagnosis and death, or date of last follow-up. Disease-free survival (DFS) was defined as the time between the date of histologic diagnosis and the date of pathologic confirmed recurrence or date of last follow-up, whichever occurred first. Whenever possible, 5-year OS and DFS rates were calculated. BODY COMPOSITION MEASUREMENT SMM was measured as muscle cross-sectional muscle area (CSA) on pre-treatment CT or MRI imaging of the head and neck area at the level of the third cervical vertebrae (C3). The axial slide of the imaging which showed both transverse processes and the entire vertebral arc 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 spe - cific for muscle tissue. 28 For MRI, muscle area was manually segmented, and fatty tissue was manually excluded. The overall intraclass correlation coefficient for the muscle CSA obtained by CT and MRI is excellent (0.97, p<0.01) (unpublished data). The CSA was calculated as the sum of the delineated areas of the paravertebral muscles and both sternocleidomastoideus muscles. An example of segmentation at the level of C3 is shown in figure 1. Figure 1. Example of segmentation of skeletal muscle tissue at the level of the third cervical vertebra (C3) Figure shows two identical axial CT-slides at the level of C3; left shows the muscle tissue unsegmented, right shows both sternocleidomastoideus and paravertebral muscles segmented in red. Segmentation of muscle tissue was manually performed using the commercially available soft - ware package SliceOmatic (Tomovision, Canada) by a single researcher (N.C). CSA at the level of C3 was converted to CSA at the level of L3 using a previously published formula, as shown in formula 1. 25 The lumbar skeletal muscle index (LSMI) was calculated by correcting SMM at 16