This study provides a comprehensive evaluation of the technical performance of CT-based L3 skeletal muscle index (L3SMI) assessment, an imaging-derived body composition biomarker increasingly used to evaluate sarcopenia and body composition in oncology. By examining accuracy, reproducibility, linearity, and repeatability across multiple cancer populations, the work demonstrates the robustness of automated skeletal muscle measurements while identifying technical limitations and exclusion criteria that can impact reliable assessment.

These findings offer practical guidance for the integration of L3SMI into clinical research and oncology development programs. By establishing performance benchmarks and highlighting conditions that may affect measurement quality, the study helps sponsors, CROs, and imaging teams improve standardization, strengthen biomarker reliability, and increase confidence in the use of body composition endpoints for patient monitoring, stratification, and longitudinal treatment evaluation.