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. 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 for anal cancer 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. Sometimes, doctors use some newer techniques that let doctors 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 it 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 at the cancer from several angles, the intensity (strength) of the beams can be adjusted to minimize 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 radiation therapy 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)
- Temporary anal irritation and pain
- Discomfort during bowel movements
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 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 and pain.
Radiation can also cause infertility in both women and men. In women, it can also lead to vaginal dryness and even cause scar tissue to form in the vagina The scar tissue can make the vagina shorter or more narrow (called vaginal stenosis), which can make sex (vaginal intercourse) painful. A woman can help prevent this problem by stretching the walls of her vagina several times a week. This can be done by using a vaginal dilator (a plastic or rubber tube used to stretch out the vagina).
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. This can lead to problems with abnormal swelling in the legs, called lymphedema. Radiation to groin lymph nodes isn’t 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.
For more information about radiation, see Understanding Radiation Therapy: A Guide for Patients and Families.
Last Medical Review: 01/02/2013
Last Revised: 01/02/2013