How does radiation therapy work?

All cells grow and divide to form new cells. But cancer cells grow and divide faster than many of the normal cells around them.

Radiation therapy uses special equipment to send high doses of radiation to the cancer cells. It damages cancer cells and causes them to die. Radiation works by breaking a piece of the DNA molecule inside the cancer cell. This break keeps the cell from growing, dividing, and spreading. Nearby normal cells also may be affected by radiation, but most recover and go back to working the way they are supposed to.

Unlike chemotherapy, which exposes the whole body to cancer-fighting drugs, radiation therapy is usually a local treatment. It’s aimed at and affects only the part of the body being treated. The goal of radiation treatment is to damage as many cancer cells as possible, with little harm to nearby healthy tissue.

Some treatments involve radioactive substances that are given in a vein or by mouth. In that case, the radiation does travel throughout the body. But for the most part, the radioactive substance collects in the area of the tumor, so there’s little effect on the rest of the body.