How does radiation therapy work?

Radiation therapy works by damaging the DNA inside cancer cells. According to the National Cancer Institute, at high doses radiation therapy kills cancer cells or slows their growth by damaging their DNA. Cancer cells whose DNA is damaged beyond repair stop dividing or die. When the damaged cells die, they are broken down and removed by the body.

Radiation therapy does not kill cancer cells right away. It takes days or weeks of treatment before the DNA is damaged enough for cancer cells to die. Then, cancer cells keep dying for weeks or months after radiation therapy ends.

There are two main types: external beam radiation, which comes from a machine that aims radiation at your cancer, and internal radiation, in which a source of radiation is placed inside your body. Your healthcare team can explain which type is planned for you and why.