151751-Najiba-Chargi

46 CHAPTER 3 Research on skeletal muscle mass (SMM) has increasingly gained interest over the past several decades. Pre-treatment low SMM, often referred to as sarcopenia, has shown to be a predictive and prognostic factor in a variety type of cancers. 1–6 In head and neck cancer (HNC), sarcopenia has shown to be a predictive factor for dose-limiting toxicity 7,8 and for the development of fistulas after total laryngectomy. 9,10 Sarcopenia has also shown to have negative prognostic impact in HNC patients. 11-13 Computed tomography (CT) has become the most used imaging modality in research on SMM because of relatively easy, fast and accurate segmentation of muscle by use of themuscle spe- cific radiodensity range of -29 to +150 Hounsfield units (HU). Currently, the most usedmethod is to assess SMM on abdominal CT, which uses the axial slice at the level of the third lumbar vertebra (L3) for segmentation of abdominal muscles as cross-sectional area (CSA). However, abdominal CT imaging is not routinely performed in HNC patients and is often only available in patients with advanced disease. Measurements of CSA of both sternocleidomastoid muscles and the paravertebral muscles at the level of the third cervical vertebra (C3) have shown to correlate well with CSA measurements at the level of L3. 17 In order to avoid selection bias in research on SMM in HNC, measurement at the level of C3 is the preferred method. 17 Magnetic resonance imaging (MRI) does not allow for segmentation of muscle tissue based on a muscle specific radiodensity range, and therefore it is subject to the interpretation of the observer. However, MRI is considered one of the most accurate methods for analyzing quantitative and qualitative changes in body composition and is associated with an error in quantifying muscle that ranges between 1.1% and 4.4%. 14 CT, like MRI, is also considered as a highly precise imaging modality in investigating human body composition and has a reported precision error of about 1.4% for tissue areas. 15 Both scanning methods are able to distinguish muscle mass from fat. CT imaging can reveal fat infiltration withinmuscle by identifying areas in the range of −190 to −30HU. 16 In the management of HNC, not all patients receive routinely CT scans. A large proportion of HNC patients receive MRI only. The agreement of CSA measurements of skeletal muscle mass (SMM) based on CT and MRI at the level of C3 is unknown. In order for SMM to be analyzed and routinely (without additional imaging and eventually retrospectively) used in the clini - cal practice of oncologic patients, it is paramount to study the concordance between SMM measurements based on CT and MRI. For this reason, we investigated the correlation in CSA measurements of SMM on CT and MRI in HNC patients. We conducted a brief retrospective study in patients with oropharyngeal squamous cell carci - noma (OPSCC), who were diagnosed and treated at the University Medical Center Utrecht, The Netherlands, between 2010 and 2015. Patients were included if they had pretreatment head and neck CT and MRI imaging of sufficient quality performed within 1 month of each other.