Britannica Sources used in this answer

How can radiation therapy destroy cancer cells?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Precancerous growth in a human colon — cancer View through an endoscope of a polyp, a benign precancerous growth projecting from the inner lining of the colon.

Radiation therapy destroys cancer cells primarily by causing significant damage to their DNA. When ionizing radiation—such as X-rays, gamma rays, or particle beams—passes through tissue, it either directly disrupts molecular structures or produces free radicals that break DNA strands within the cell [nucleus].12

This genetic damage prevents cancer cells from replicating, leading to their death, or triggers apoptosis (programmed cell death). Cancer cells are particularly vulnerable to this process because they are continuously proliferating, which makes them less capable of recovering from radiation-induced injury compared to healthy, non-dividing cells.134

Because radiation is administered in repeated small doses, known as fractions, it allows for the effective treatment of malignant disease while minimizing complications in surrounding healthy tissues. In some cases, this therapy is used to shrink tumors to relieve symptoms or is combined with surgery to eradicate undetected cells at a tumor's periphery.32