Cross-sectional and longitudinal assessment of muscle from regular chest computed tomography scans: L1 and pectoralis muscle compared to L3 as reference in non-small cell lung cancer

Background: Computed tomography (CT) is increasingly used in clinical research for single-slice assessment of muscle mass to correlate with clinical outcome and evaluate treatment efficacy. The third lumbar level (L3) is considered as reference for muscle, but chest scans generally do not reach beyond the first lumbar level (L1). This study investigates if pectoralis muscle and L1 are appropriate alternatives for L3. Methods: CT scans of 115 stage IV non-small cell lung cancer patients were analyzed before and during tumor therapy. Skeletal muscle assessed at pectoralis and L1 muscle was compared to L3 at baseline. Furthermore, the prognostic significance of changes in muscle mass determined at different locations was investigated. Results: Pearson's correlation coefficient between skeletal muscle at L3 and L1 was stronger (r=0.90, P<0.001) than between L3 and pectoralis muscle (r=0.71, P<0.001). Cox regression analysis revealed that L3 (HR 0.943, 95% CI: 0.92-0.97, P<0.001) and L1 muscle loss (HR 0.954, 95% CI: 0.93-0.98, P<0.001) predicted overall survival, whereas pectoralis muscle loss did not. Conclusion: L1 is a better alternative than pectoralis muscle to substitute L3 for analysis of muscle mass from regular chest CT scans.