Radiation therapy is used to treat cancer. Radiation therapy uses high-energy radiation to kill cancer cells and try to stop or slow further growth of the cancer. Radiation treatment is administered to a specific area of the body, so it is most useful for cancer that has not spread throughout the body.
Some kinds of radiation penetrate more deeply into the body than can others. In addition, some types of radiation can be very controlled to treat only a small area (an inch of tissue, for example) without damaging nearby tissues and organs. Other types of radiation are better for treating larger areas.
In some cases, the goal of radiation treatment is the complete destruction of an entire tumor. In other cases, the aim is to shrink a tumor and relieve symptoms. In either case, doctors plan treatment to spare as much healthy tissue as possible.
About half of all people who have cancer receive some type of radiation therapy. Radiation therapy may be used alone or in combination with other cancer treatments, such as chemotherapy or surgery. A person may receive more than one type of radiation therapy.
Radiation can be applied externally or internally. External radiation is most common. It comes from a machine outside the body, and is usually given on an outpatient basis. Internal radiation is implanted into or near the tumor in small capsules or other containers. It may require a hospital stay.
Sources of Energy for External Radiation Therapy
The energy (source of radiation) used in external radiation therapy may come from the following:
- X-rays or gamma rays, which are both forms of electromagnetic radiation. Although they are produced in different ways, both use photons (packets of energy). X-rays are created by machines called linear accelerators. Depending on the amount of energy the x-rays have, they can be used to destroy cancer cells on the surface of the body (lower energy) or deeper into tissues and organs (higher energy). Compared with other types of radiation, x-rays can deliver radiation to a relatively large area. Gamma rays are produced when isotopes of certain elements (such as iridium and cobalt 60) release radiation energy as they break down. Each element breaks down at a specific rate and each gives off a different amount of energy, which affects how deeply it can penetrate into the body.
- Particle beams use fast-moving subatomic particles instead of photons. This type of radiation may be called particle beam radiation therapy or particulate radiation. Unlike x-rays and gamma rays, some particle beams can penetrate only a short distance into tissue. Therefore, they are often used to treat cancers located on the surface of or just below the skin.
- Proton beam therapy is a type of particle beam radiation therapy. Protons deposit their energy over a very small area, which is called the Bragg peak. The Bragg peak can be used to target high doses of proton beam therapy to a tumor while doing less damage to normal tissues in front of and behind the tumor. Proton beam therapy is available at only a few facilities in the United States.