This page discusses the use of radiation therapy for the treatment of colorectal cancer. For a thorough review of radiation therapy for cancer treatment, please see the radiation therapy treatment monograph .

Radiation therapy is the use of penetrating beams of high-energy waves or streams of particles called radiation to treat disease. Radiation therapy destroys the ability of cancer cells to grow and divide. Colon cancer can be treated with external radiation therapy.

External Radiation Therapy

In external radiation therapy, rays are directed at the tumor from outside the body.

Like chemotherapy, the side effects from radiation result from injury to the normal tissues. There are many new ways that the radiation oncologist can customize your treatment to try to kill as many of the cancer cells while sparing as much normal tissue as possible.

The radiation oncologist will determine how many treatments you will receive; sometimes they will be once a day and sometimes twice per day. Each treatment generally only takes a few minutes, and the total treatment time can range from five to eight weeks depending on the total dose required.

Use and Effectiveness

Radiation therapy is commonly used in rectal cancer, and less commonly used in colon cancer.

In rectal cancer, radiation therapy is used whenever the cancer has been found to extend beyond the muscular layer of the bowel, and into the fat or thin skin around the rectum. It is also given whenever the lymph nodes have cancer in them. In this situation, radiation can be given either before or after surgery, and is often delivered along with chemotherapy. Radiation therapy can reduce the chances that the cancer will come back as well as improve overall survival.

In colon cancer, radiation is used or considered whenever the surgeon has to leave some cancer behind or when the cancer has spread to adjacent structures (small intestine or abdominal wall).

Side Effects

Side effects of radiation therapy specific to colon cancer include the following:

  • Appetite loss
  • Nausea, vomiting, or diarrhea
  • Mouth ulcers
  • Difficulty swallowing

Tell your doctor if you experience these side effects, so that steps can be taken to reduce your discomfort. Many side effects can be controlled with medication or diet. If the side effects are dramatic, your doctor may alter or delay the course of your treatment. After treatment, most side effects will gradually diminish and disappear.

For more information on radiation therapy including how to manage side effects, see the radiation therapy treatment monograph .