151751-Najiba-Chargi

69 Diagnostics: measuring skeletal muscle mass of the musculus masseter DISCUSSION Patients with head and neck cancers are at an increased risk of sarcopenia compared to pa- tients with other types of cancer. 8,9,26 Previous reports have established that measuringmuscle mass at the level of L3 on CT-scans is a reliablemethod for assessing total body skeletal muscle mass. Unfortunately, scans at this lumbar level are rarely available in patients with HNSCC. Previously published findings by Swartz et al. show that the CSA of skeletal muscles at level of C3 strongly correlates with the CSA of skeletal muscles at the level of L3, indicating that this is a viable alternative method. However, determining the CSA at C3 is time consuming and can be impacted by either treatment (e.g., neck dissection) or disease (e.g., invading lymph node in the SCM). We therefore investigated to what degree masseter muscle parameters are asso - ciated with levels L3 and C3, and their relationship on overall survival. We found moderate to strong associations for most masseter parameters with muscle mass on level L3 and C3, with MV being the strongest followed by masseter CSA. LowMSMI was shown to be an independent prognostic for decreased overall survival in multivariate analysis. We found that the scatter-score had a significant impact on MV and masseter HU measure - ments. It stands to reason that scattering results in unreliablemasseter HU-measurements, as scattering generally causes a larger spread of pixel values shown on imaging. The method we used to determine MV used the Tumor Tracking feature included in IntelliSpace which utilizes the pixel values recorded and inputs them into an algorithm to determine whether certain areas are related to each other. It follows that a larger spread in pixel-values decreases the reliability of the algorithm. Manual adjustment of the measured area was often required to fully include all masseter muscle tissue, although this too becomes unreliable when significant scattering is present. However, we found no significant relationship between scatter-score and MT, HU ROI and MCSA (and subsequently MSI) leaving these as viable options when significant scattering is present. Our included patient group had 8 (7.1%) patients with tumors in the oral cavity. Based on expert opinion none of those significantly impacted the masseter muscle. If present, one solution could be that in the rare cases where the muscle is unilaterally signifi- cantly affected, a contralateral masseter measurement is counted twice. Our findings are consistent with other studies which determine that masseter CSA predicts mortality in patients suffering fromblunt trauma, traumatic brain injury or undergoing carotid endarterectomy. 19–21 However, differences between our study and earlier scientific reports should be noted. Oksala et al, Wallace et al and Hu et al. all used the masseter CSA measured at 2cm below the arcus zygomaticus. In our study, we chose the first slice showing the dens of the C2 vertebra as our landmark as this was easily identifiable when scrolling in cepha- lad-to-caudad fashion. Secondly, whereas Wallace et al. and Hu et al. did not correct for head tilt, Oksala et al. adjusted their CT-scans for both sagittal and coronal head tilt. Based on expert opinion we chose to 4