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.

Types of Radiation Therapy That Treat Cancer

Cancer patients receiving radiation therapy are often concerned that the treatment will make them radioactive. The answer to this question depends on the type of radiation therapy being given.

External radiation therapy will not make the person radioactive. You do not need to avoid being around other people because of the treatment.

Internal radiation therapy that involves sealed implants emits radioactivity, so a stay in the hospital may be needed. Certain precautions are taken to protect hospital staff and visitors. The sealed sources deliver most of their radiation mainly around the area of the implant, so while the area around the implant is radioactive, the person's whole body is not radioactive.


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Systemic radiation therapy uses unsealed radioactive materials that travel throughout the body. Some of this radioactive material will leave the body through saliva, sweat, and urine before the radioactivity decays, making these fluids radioactive. Therefore, certain precautions are sometimes used for people who come in close contact with the person. The doctor or nurse will provide information if these special precautions are needed.

The Radiation Treatment Team

Many health care providers help to plan and deliver radiation treatment to the patient. The radiation therapy team includes the surgeon, radiologist (a doctor who specializes in creating and interpreting pictures of areas inside the body), pathologist (a doctor who identifies diseases by studying cells and tissues under a microscope), and others to plan the patient's total course of therapy.

Because there are so many types of radiation and many ways to deliver it, treatment planning is a very important first step for every patient who will have radiation therapy. Before radiation therapy is given, the patient's radiation therapy team determines the amount and type of radiation the patient will receive.


The National Cancer Institute which conducts and supports research, training, health information dissemination, and other programs with respect to the cause, diagnosis, prevention, and treatment of cancer, rehabilitation from cancer, and the continuing care of cancer patients and the families of cancer patients.