What is radiation therapy?

Abramson Cancer Center of the University of Pennsylvania
Last Modified: November 1, 2001

Radiation is a type of high energy that comes from special machines (i.e., X-ray machines) or radioactive sources (i.e., cobalt, radioactive iodine). When used at high doses, radiation can destroy cells or keep them from growing or dividing. The use of high-energy rays or particles to treat disease is called radiation therapy. You may also hear it referred to as x-ray therapy, cobalt therapy, or irradiation.

Radiation therapy is an effective way to treat many kinds of cancer in almost any part of the body. About half of all patients with cancer are treated with radiation. For some, radiation therapy is the only treatment necessary. For others, radiation therapy is combined with other treatments, such as surgery and chemotherapy, to best treat their cancer.

Radiation works best against cells that are growing and dividing. Because cancer cells grow and divide more rapidly than many of the normal cells around them, radiation therapy is a useful tool in treating cancer. Although some of the healthy cells in the area where the radiation is given are also destroyed, most normal cells tend to recover more quickly and more fully from the effects of radiation than do the cancer cells. Careful planning is taken to ensure that the radiation affects as little of the normal tissue as possible.

How is radiation therapy given?

Radiation therapy can be given either externally or internally. Most patients who receive radiation therapy receive it externally. In this type of treatment, doses of radiation are given to a carefully defined area through a machine that directs the high-energy rays or particles at the cancer and the normal tissue surrounding it. Treatments are usually given once a day, Monday through Friday, over a period of 3 to 7 weeks. Patients normally receive each treatment during an outpatient visit to a hospital or radiation therapy treatment center, and very few require an in-patient admission. Since the radiation is given in relatively small doses, patients who receive external radiation therapy are not considered radioactive and do not need to take any special precautions during the time they are being treated.

Radiation therapy can also be given internally to administer higher doses of radiation directly to the tumor. In some cases, the radioactive substance is sealed in small containers such as thin wires or tubes, which are held in place by mechanical devices. In other situations, the radioactive substance is swallowed by mouth or injected into the body. These are referred to as unsealed sources. Most patients who receive internal radiation therapy are admitted to the hospital for 3-7 days. For more information on internal radiation therapy, go to Internal Radiation Therapy.

There are two types of machines that are used to deliver external radiation therapy. One is a linear accelerator, a machine that creates high-energy radiation using electricity to form a stream of fast-moving subatomic particles. The other type of machine contains a radioactive substance, most often cobalt-60, as its source of radiation. The Department of Radiation Oncology at the Abramson Cancer Center of the University of Pennsylvania uses state-of-the-art linear accelerators. These machines deliver the radiation therapy to the tumor with great accuracy, killing the cancer while sparing as much of the surrounding healthy tissue as possible. For more information on external radiation therapy, go to Overview of the Treatment Process.