# Clinical impact of computed tomography-measured skeletal muscle status at the third cervical vertebra on definitive radiotherapy outcomes for head and neck squamous cell carcinoma

## TL;DR

This study shows that lower skeletal muscle area at the C3 vertebra on CT scans predicts worse survival in head and neck cancer patients undergoing radiotherapy.

## Contribution

Demonstrates that low skeletal muscle area at C3 is an independent predictor of survival in HNSCC patients receiving definitive radiotherapy.

## Key findings

- Low skeletal muscle area (SMA) at C3 was significantly associated with poorer overall survival in univariate analysis.
- Low SMA remained an independent predictor of reduced overall survival in multivariate analysis.
- The 3-year overall survival rate for the entire cohort was 81.6%.

## Abstract

Loss of skeletal muscle mass is increasingly recognized as a poor prognostic indicator in patients with cancer, including those with head and neck squamous cell carcinoma (HNSCC). Emerging evidence suggests that the muscle area measured at the third cervical vertebra (C3) on CT serves as a practical surrogate for whole-body muscle status. This study aimed to evaluate the prognostic significance of C3-level body composition parameters in patients with HNSCC undergoing definitive radiotherapy.

A total of 283 consecutive patients with HNSCC treated with definitive radiotherapy between 2013 and 2023 were retrospectively analyzed. Pre-treatment CT scans were used to assess six body composition metrics at the C3 level: skeletal muscle area (SMA), mean skeletal muscle density, visceral adipose tissue area, subcutaneous adipose tissue area, visceral-to-subcutaneous fat ratio, and skeletal muscle fat infiltration index. Patients were stratified into high and low groups based on sex-specific median values. Associations between each body composition metric (high vs. low) and survival outcomes were assessed using univariate and multivariate analyses.

The cohort included 238 males and 45 females, with a median age of 67 years. Survival analysis showed a median follow-up period of 39.3 months. The 3-year overall survival (OS) rate for the entire cohort was 81.6%, and the 3-year progression free survival rate was 60.8%. In univariate analysis, only low SMA was significantly associated with poorer OS (hazard ratio: 1.841, p = 0.027). The median SMA was 35.0 cm2 for males and 23.5 cm2 for females. 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.

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. These findings support the clinical relevance of SMA assessment as a straightforward and robust prognostic biomarker and underscore the need for further investigation into the prognostic potential of other body composition metrics.