Radiation therapy uses a beam of high-energy rays (or particles) to destroy cancer cells or slow their rate of growth. Sometimes doctors give radiation to shrink a tumor so that it can be removed more easily during surgery. There are 2 major forms of radiation therapy: external beam and brachytherapy.

External-beam radiation therapy (EBRT)

The most common way to deliver radiation is to use a focused beam of radiation from a machine outside the body. This is known as external-beam radiation therapy. Treatments are usually given 5 days a week for a period of 5 weeks or so.

Radiation can harm nearby healthy tissue along with the cancer cells. To reduce the risk of side effects, doctors carefully figure out the exact dose you need and aim the beam as accurately as they can.

Side effects of radiation therapy vary based on the area of the body treated and the dose of radiation given. Skin changes (like a sunburn) are common and improve after radiation is stopped. Temporary anal irritation and pain with discomfort during bowel movements may also occur. Other possible side effects include fatigue, nausea, or diarrhea. Long-term side effects can also occur. Damage to anal tissue by radiation may cause scar tissue to form. This scar tissue can sometimes keep the anal sphincter from working as it should. Radiation to the pelvis can weaken the bones, increasing the risk of fractures of the pelvis or hip. Radiation can also damage blood vessels that nourish the lining of the rectum and lead to chronic radiation proctitis (inflammation of the lining of the rectum). This can cause rectal bleeding.

The radiation field may include some of the pelvis in order to treat lymph nodes in the groin, because the cancer will often spread to these lymph nodes. Doctors aren't sure this is always needed. People with small tumors may not need radiation therapy to the groin lymph nodes because the cancer is less likely to spread. If the doctors think the cancer has spread to the lymph nodes, because they are enlarged, then they will either treat them with radiation therapy or surgery.

Internal radiation (Brachytherapy)

Another method of delivering radiation is to place small sources of radioactive materials in or near the tumor. This method, internal radiation, concentrates the radiation in the area of the cancer. It is also called brachytherapy, interstitial radiation, and intracavitary radiation. This may involve implanting permanent radioactive pellets, or "seeds," which release their dose slowly over time, or other techniques where the radioactive substance is in the body for only a brief period. Internal radiation can be more convenient because it usually requires only one or a few sessions, but it may require some type of surgery.

Brachytherapy is used much less often than external-beam radiation therapy to treat anal cancer. When it is used, it is usually given along with external radiation. The possible side effects are often similar to those seen with external radiation.

Last Medical Review: 08/17/2009
Last Revised: 08/17/2009