Radiobiology

Radiobiology is the scientific study of the effects of ionizing radiation on living organisms. It covers the initial physical interactions of radiation with biological matter, the subsequent chemical and biological processes, and the cellular, tissue, and organism-level outcomes. Radiobiology encompasses laboratory studies, clinical radiology, radiation protection, and radiation physics, and informs how radiation is used in medicine and industry. Ionizing radiation includes electromagnetic radiation such as X-rays and gamma rays, and particulate radiation such as alpha and beta particles and neutrons.

At the cellular level, radiation can cause DNA damage, most notably double-strand breaks, which may be repaired or lead to cell death, senescence, or chromosomal abnormalities. Cells exhibit varying radiosensitivity depending on type, phase of the cell cycle, and microenvironment. Repair mechanisms include non-homologous end joining and homologous recombination. Dose-response relationships describe how biological effects scale with absorbed dose. Low to moderate doses raise cancer risk in a stochastic manner and without a clear threshold, though high doses can produce deterministic effects with thresholds, such as skin erythema or acute radiation syndrome. Dose is measured in Gray (Gy); effect is weighted to yield Sievert (Sv) for risk assessments; absorbed dose, equivalent dose, and effective dose reflect radiation quality and tissue sensitivity. Relative biological effectiveness (RBE) and linear energy transfer (LET) describe how different radiations differ in biological impact.

Applications include radiotherapy for cancer, diagnostic radiology and imaging, and radioprotection to prevent harmful exposure in medical, occupational, and environmental contexts. Radiobiology also studies animal and cell models to understand mechanisms and supports space radiation research and emergency response planning. Notable milestones include early X-ray discovery and subsequent work showing radiation-induced mutations, shaping safety standards and medical practice.