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Radiation treatment is the use of high-energy rays (such as x-rays) to kill cancer cells or shrink tumors.

When is radiation used?

Before surgery: If the size of a tumor or where it is makes it hard to take it out, radiation may be used before surgery to shrink the tumor. Radiation is also used sometimes before surgery for rectal cancers, because it lowers the risk of the cancer coming back later. When it is used for rectal cancers before surgery, radiation is often combined with chemotherapy. This is called chemoradiation. The chemo helps the radiation work better, but adds to the side effects.

After surgery: Radiation can also be used after surgery, to kill any cancer cells that may have been left behind (but couldn’t be seen). This lowers the chance that the cancer will come back later.

For people who can’t have surgery: Radiation can be given to help control rectal cancers in people who are not healthy enough for surgery.

For advanced cancers: Radiation can also be used to ease symptoms of advanced cancer, such as intestinal blockage, bleeding, or pain. It is also be used to treat colon cancer that has spread, most often if the spread is to the bones or the brain.

Types of radiation treatment

In the most common type of radiation used to treat colorectal cancer, radiation is focused on the cancer from a machine outside the body. This is called external beam radiation therapy.

Radiation can also be given to the rectum with a small device that is placed through the anus and into the rectum. This is called endocavitary radiation therapy.

Another way to treat rectal cancers is to place small pellets or seeds of radioactive material into a tube or container so that they are next to or right into the cancer. This is called brachytherapy.

Side effects of radiation therapy

Some of the common side effects of radiation therapy for colon or rectal cancer include:

  • Skin changes in the area where the radiation passes
  • Nausea and vomiting
  • Diarrhea
  • Rectal irritation, which can lead to trouble controlling your bowels
  • Bladder irritation which can make you feel like you have to pass urine often
  • Tiredness.

Sexual problems may also occur.

Side effects often go away or lessen over time after treatment is finished, but problems such as rectal and bladder irritation may remain. If you have these or other side effects, talk to your doctor. There are often ways to reduce or relieve many of these problems.

More detailed information about radiation for colorectal cancer can be found in Colorectal Cancer.

You can also learn more about radiation in Radiation Therapy – What It Is, How It Helps.

Last Medical Review: 10/15/2014
Last Revised: 02/26/2016