BIOLOGICAL EFFECTS OF IONIZING RADIATION

Abstract

Ionizing radiation is used widely in medicine, industry, and research, yet the same physical property that makes it diagnostically and therapeutically useful—its ability to deposit energy in tissues—also underlies biological harm. The biological effect of ionizing radiation is not a single phenomenon but a cascade that begins with physical interactions (ionization and excitation), proceeds through chemical stages (radiolysis of water and reactive oxygen species generation), and culminates in molecular lesions, cellular responses, tissue injury, and long-term health outcomes. This article synthesizes the modern view of radiation effects by integrating mechanisms of DNA damage and repair, radiation quality and dose-rate modifiers, deterministic tissue reactions with thresholds, and stochastic effects such as carcinogenesis and heritable risk. Particular attention is given to radiosensitivity differences among organs and life stages, the clinical context of diagnostic imaging and radiotherapy, and practical risk management through justification and optimization. The review argues that meaningful safety is achieved when protocols are aligned with the clinical question, dose is minimized without compromising diagnostic value, and patient-specific factors are considered systematically. The ALARA principle, diagnostic reference levels, and quality assurance are discussed as operational tools to translate radiobiological knowledge into safer practice.