151751-Najiba-Chargi

422 CHAPTER 21 SUMMARIZING DISCUSSION This thesis presents research that focuses on diagnostic measurements of skeletal muscle mass and to evaluate the predictive and prognostic value of low skeletal muscle mass in pa- tients with head and neck cancer. Besides radiologically assessed skeletal muscle mass at di - agnosis, the impact of muscle function, especially in the elderly head and neck cancer patients, is investigated. The results of this thesis lead to improved pre-treatment risk-stratification, development of personalized treatment protocols, improved prediction of prognosis and last but not least improved shared decision-making. Research on skeletal musclemass as a biomarker is increasing the last decade due to improved diagnostics in clinical practice. Measurement of lean body mass, of which skeletal muscle mass is the largest contributor, is in clinical practice mostly performed with the use of dual x-ray absorptiometry (DEXA) and bioelectrical impedance (BIA). These diagnostic tools are however confounded by alterations in hydration, edema and food intake. Therefore, its use in assessing body composition of patients with cancer is not favored. Research on body com - position, specifically skeletal muscle mass, is mostly performed on computed tomography (CT) imaging because of relatively ease, fast and accurate segmentation of muscle by use of the muscle-specific radiodensity range of -29 till +150 Hounsfield units (HU). An advantage of using skeletal muscle mass as a biomarker in clinical practice is that it can be evaluated by the use of already available CT imaging that are routinely obtained for head and neck cancer diagnosis and treatment evaluation. Skeletal muscle mass is determined by segmenting the area of skeletal muscles visible on one specific two-dimensional axial slice. 1 The most used landmark on CT for muscle segmentation is at the level of the third lumbar vertebrae (L3) visible on abdominal CT imaging, in which the area of the psoas, erector spinae, quadratus lumborum, transversus abdominis, external and internal obliques and rectus abdominis muscles is segmented. Previous studies showed that there is a linear relationship between a person’s height and the skeletal muscle area at the level of L3, therefore the obtained skeletal muscle area is adjusted for height, to calculate the lumbar skeletal muscle mass index (SMI in cm 2 /m 2 ). 2,3 The SMI provides an estimation of total skeletal muscle mass in proportion to stature. The first described study that performed skeletal muscle mass segmentation on CT to evaluate the relationship between body com- position and adverse outcomes in patients with cancer is performed in 2008 by Prado et al. 2 In head and neck cancer, abdominal CT imaging is only performed in patients with locally advanced cancer for staging purposes. Therefore, a previous study by Swartz et al. developed a measurement method of skeletal muscle mass at the level of the third cervical vertebrae (C3) which is visible on head and neck CT imaging. 4 Part I of this thesis presents the studies performed to further evaluate the skeletal muscle mass measurement at this level (C3) in head and neck cancer patients. In Chapter 2, a validation study is performed for skeletal muscle mass measurements at the level of C3 and L3 in order to validate the results found in