Radiation Therapy for Anal Cancer

Radiation therapy uses a beam of high-energy rays (or particles) to destroy cancer cells or slow their rate of growth. Radiation therapy can be used:

  • As part of the main treatment (along with chemotherapy) for most anal cancers
  • After surgery if the doctor is concerned that all of the cancer might not have been removed
  • To help treat cancer that has returned in the lymph nodes after initial treatment
  • To help control advanced cancer or to relieve symptoms it causes

There are 2 main forms of radiation therapy: external beam and internal radiation (brachytherapy).

External-beam radiation therapy (EBRT)

The most common way for anal cancer to be treated with radiation is with a focused beam of radiation from a machine outside the body. This is known as external-beam radiation therapy.

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 beams as accurately as they can. Before your treatments start, the radiation team will get CT or MRI scans of the area to be treated to help figure this out. Radiation therapy is much like getting an x-ray, but the radiation is stronger. The procedure itself is painless. Each treatment lasts only a few minutes, although the setup time – getting you into place for treatment – usually takes longer. Treatments are usually given 5 days a week for a period of 5 weeks or so.

Doctors often use newer techniques that let them give higher doses of radiation to the cancer while reducing the radiation exposure to nearby healthy tissues.

Three-dimensional conformal radiation therapy (3D-CRT) uses special computers to precisely map the location of your cancer. Radiation beams are then shaped and aimed at the tumor from several directions, which makes them less likely to damage normal tissues. You will most likely be fitted with a plastic mold resembling a body cast to keep you in the same position each day so that the radiation can be aimed more accurately. This method seems to be at least as effective as standard radiation therapy for anal cancer and may have lower side effects.

Intensity-modulated radiation therapy (IMRT) is an advanced form of 3D therapy. It uses a computer-driven machine that actually moves around the patient as it delivers radiation. In addition to shaping the beams and aiming them from several angles, the intensity (strength) of the beams can be adjusted to limit the dose reaching the most sensitive normal tissues. This lets doctors deliver an even higher dose to the cancer areas. It is available at many major hospitals and cancer centers.

Side effects of external radiation therapy

Side effects vary based on the area of the body treated and the dose of radiation given. Some common short-term side effects include:

  • Skin changes (like a sunburn) in areas being treated
  • Temporary anal irritation and pain
  • Discomfort during bowel movements
  • Fatigue
  • Nausea
  • Diarrhea

In women, radiation may irritate the vagina. This can lead to discomfort and drainage (a discharge).

These side effects often improve after radiation stops.

Long-term side effects can also occur:

  • Damage to anal tissue by radiation may cause scar tissue to form. This can sometimes keep the anal sphincter from working as it should, which could lead to problems having bowel movements.
  • Radiation to the pelvis can weaken the bones, increasing the risk of fractures of the pelvis or hip.
  • Radiation can 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 and pain.
  • Radiation can affect fertility (the ability to have children) in both women and men. (For more information, see Fertility and Men With Cancer and Fertility and Women With Cancer.)
  • Radiation can lead to vaginal dryness and even a narrowing or shortening of the vagina (called vaginal stenosis), which can make sex painful. A woman can help prevent this problem by stretching the walls of her vagina several times a week. This can be done using a vaginal dilator (a plastic or rubber tube used to stretch out the vagina). (For more information, see Sexuality for the Woman With Cancer.)
  • If radiation is given to the lymph nodes in the groin, it can lead to problems with abnormal swelling in the legs, called lymphedema. (For more information, see For People at Risk of Lymphedema

Internal radiation (brachytherapy)

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

The possible side effects are often similar to those seen with external radiation.

More information on radiation as a treatment for cancer can be found in the Radiation Therapy section of our website.

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: April 9, 2014 Last Revised: January 20, 2016

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