How does radiation therapy work?

Radiation therapy uses special equipment to send high doses of radiation to the cancer cells.

Most cells in the body grow and divide to form new cells. But cancer cells grow and divide faster than many of the normal cells around them. Radiation works by making small breaks in the DNA inside cells. These breaks keep cancer cells from growing and dividing, and often cause them to die. Nearby normal cells can also be affected by radiation, but most recover and go back to working the way they should.

Unlike chemotherapy, which exposes the whole body to cancer-fighting drugs, in most cases, radiation therapy is 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 cancer cells, with as little harm as possible to nearby healthy cells.

Some treatments use radioactive substances that are given in a vein or by mouth. In this case, the radiation does travel throughout the body. Still, 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.

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master’s-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Last Medical Review: June 30, 2015 Last Revised: June 30, 2015

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