Electron Stopping Power in Human Body Tissues: A Systematic Review

Abstract

Electron stopping power is a fundamental parameter governing charged-particle interactions in biological matter and constitutes the physical basis of electron dosimetry in radiotherapy, diagnostic imaging, and radiation protection. Despite the widespread reliance on reference databases such as NIST ESTAR, experimental measurements of electron stopping power in human tissues and tissue-equivalent materials remain dispersed across the literature, spanning diverse energy ranges, tissue compositions, and experimental methodologies. This systematic review provides a comprehensive synthesis of experimental data on electron stopping power in human tissues and tissue-equivalent materials across the keV–MeV energy range. Following PRISMA 2020 guidelines, peer-reviewed experimental studies reporting electron stopping power or closely related quantities were systematically identified, screened, and qualitatively synthesized. Due to substantial heterogeneity in electron energies, tissue types, measurement techniques, and reported outcome metrics, quantitative meta-analysis was not justified; instead, an analytically stratified qualitative synthesis was performed with reference to NIST ESTAR data. Across all included studies, the electron stopping power consistently decreased with increasing electron energy. Soft tissues and water-equivalent materials generally exhibited good agreement with reference expectations. In contrast, mineralized tissues—particularly cortical bone—demonstrated reproducible and systematic deviations from reference data, most pronounced at lower electron energies. These deviations were observed consistently across independent studies and experimental approaches, indicating composition-driven physical effects rather than random experimental uncertainty.  The findings demonstrate that previously perceived measurement discrepancies reflect physically meaningful variations arising from tissue composition, energy regime, and experimental methodology. While reference databases remain indispensable for routine applications, their tissue- and energy-specific limitations highlight the continued need for targeted experimental investigations in biologically complex materials.