Deep Learning-Assisted Skeletal Muscle Radiation Attenuation at C3 Predicts Survival in Head and Neck Cancer

Background: Head and neck cancer (HNC) patients face an increased risk of malnutrition due to lifestyle, tumor localization, and treatment effects. While skeletal muscle area (SMA) and radiation attenuation (SM−RA) at the third lumbar vertebra (L3) are established prognostic markers, L3 is not routinely available in head and neck imaging. The prognostic value of SM−RA at the third cervical vertebra (C3) remains unclear. This study assesses whether SMA and SM−RA at C3 predict locoregional control (LRC) and overall survival (OS) in HNC. Methods: We analyzed 904 HNC cases with head and neck CT scans. A deep learning pipeline identified C3, and SMA/SM−RA were quantified via automated segmentation with manual verification. Cox proportional hazards models assessed associations with LRC and OS, adjusting for clinical factors. Results: Median SMA and SM−RA were 36.64 cm 2 (IQR: 30.12–42.44) and 50.77 HU (IQR: 43.04–57.39). In multivariate analysis, lower SMA (HR 1.62, 95% CI: 1.02–2.58, p = 0.04), lower SM−RA (HR 1.89, 95% CI: 1.30–2.79, p < 0.001), and advanced T stage (HR 1.50, 95% CI: 1.06–2.12, p = 0.02) were prognostic for LRC. OS predictors included advanced T stage (HR 2.17, 95% CI: 1.64–2.87, p < 0.001), age ≥70 years (HR 1.40, 95% CI: 1.00–1.96, p = 0.05), male sex (HR 1.64, 95% CI: 1.02–2.63, p = 0.04), and lower SM−RA (HR 2.15, 95% CI: 1.56–2.96, p < 0.001). Conclusion: Deep learning−assisted SM−RA assessment at C3 outperforms SMA for LRC and OS in HNC, supporting its use as a routine biomarker and L3 alternative.