Interobserver agreement of skeletal muscle mass measurement on head and neck CT imaging at the level of the third cervical vertebra

Objectives Skeletal muscle mass (SMM) is most often assessed in cancer patients on abdominal computed tomography (CT) imaging at the level of the third lumbar vertebra (L3). Abdominal CT imaging is not routinely performed in head and neck cancer (HNC) patients. Recently, a novel method to assess SMM on a single transversal CT slice at the level of the third cervical vertebra (C3) was published. The objective of this study was to assess the robustness of this novel C3 measurement method in terms of interobserver agreement. Patients and methods Patients diagnosed with locally advanced head and neck squamous cell carcinoma (LA-HNSCC) at our center between 2007 and 2011 were evaluated. Fifty-four patients with were randomly selected for analysis. Six observers independently measured the cross-sectional muscle area (CSMA) at the level of C3 using a predefined, written protocol as instruction. Interobserver agreement was assessed using intraclass correlation coefficients (ICCs), a Bland–Altman plot and Fleiss’ kappa (κ). Results The agreement in vertebra selection between all observers was excellent (Fleiss’ κ: 0.96). There was a substantial agreement between all observers in single slice selection (Fleiss’ κ: 0.61). For all CSMA measurements, ICCs were excellent (0.763–0.969; all p < 0.001). The Bland–Altman plot showed good agreement between measurements, with narrow limits of agreement. Conclusion Interobserver agreement for SMM measurement at the level of C3 was excellent. Assessment of SMM at the level of C3 is easy and robust and can performed on routinely available imaging in HNC patients.