Intracellular Responses to Ionizing Radiation: From Initial Damage to Cell Fate and Intercellular Communication

Ionizing radiation induces biological effects through direct energy deposition in biomolecules and indirect damage mediated by water radiolysis and reactive oxygen species. This review synthesizes the intracellular and intercellular events that connect these initial reactions to cell-fate determination. Following irradiation, cells coordinate DNA damage recognition, checkpoint control, and repair with oxidative stress and inflammatory signaling. Together, these responses connect the initial molecular damage with the intracellular and intercellular events that follow. The balance among damage severity, repair capacity, cell-cycle stage, genetic background, and microenvironmental signals shapes outcomes including recovery, transient or permanent arrest, senescence, mitotic catastrophe, apoptosis, regulated necrosis, and autophagy-associated survival or death. Irradiated cells further influence surrounding tissues through cytokines, chemokines, senescence-associated secretory factors, damage-associated molecular patterns, and cyclic GMP–AMP synthase–stimulator of interferon genes signaling. These integrated responses determine both therapeutic effects and normal-tissue injury, supporting investigation across molecular, cellular, immune, and tissue levels.