In multivariate analysis, low SMA remained an independent predictor of reduced OS (hazard ratio: 1.851, p = 0.028), along with clinical stage and chemotherapy status.<h4>Conclusion</h4>Among the CT-derived body composition parameters assessed at the C3 level, low SMA was the only significant independent predictor of OS in patients with HNSCC receiving definitive radiotherapy. Here, SMN1 is linked to head and neck squamous cell carcinoma.