How does X-ray radiation therapy destroy cancer cells?

Radiation therapy utilizes ionizing radiation, such as X-rays, to destroy cancer cells by causing significant genetic damage.12

As X-ray beams pass through tissue, they act as indirectly ionizing radiation. They impart energy to electrons, ejecting them from their orbits and creating reactive ions and [free radicals]. These byproducts, along with direct interactions, cause breaks in the double-stranded DNA within the cell nucleus.13

This damage prevents cancer cells from replicating, eventually leading to their death or triggering apoptosis (programmed cell death). Because cancer cells are continuously proliferating, they are generally more sensitive to this radiation and less capable of recovering from the damage than healthy, non-dividing cells. To maximize effectiveness while protecting surrounding healthy tissue, radiation is often administered in repeated small doses known as fractions.12