Colorectal Cancer

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Treating Colon/Rectum Cancer TOPICS

Radiation therapy for colorectal cancer

Radiation therapy uses high-energy rays (such as x-rays) or particles to destroy cancer cells. It may be part of treatment for either colon or rectal cancer. Chemotherapy can make radiation therapy more effective against some colon and rectal cancers. Using these 2 treatments together is known as chemoradiation or chemoradiotherapy.

Radiation therapy is mainly used in people with colon cancer when the cancer has attached to an internal organ or the lining of the abdomen. When this occurs, the surgeon cannot be certain that all the cancer has been removed, and radiation therapy may be used to try to kill any cancer cells that may be left behind after surgery.

Radiation therapy is also used to treat colon cancer that has spread, most often if the spread is to the bones or brain.

For rectal cancer, radiation therapy is usually given either before or after surgery to help prevent the cancer from coming back in the area where the tumor started. It is often given along with chemotherapy. Many doctors now favor giving radiation therapy before surgery, as it may make it easier to remove the cancer, especially if the cancer's size and/or position may make surgery difficult.

Giving radiation before surgery may lower the risk that the tumor will come back (recur) in the pelvis. It may also result in fewer complications such as scar formation that can cause problems with bowel movements. Radiation therapy can also be given to help control rectal cancers in people who are not healthy enough for surgery or to ease (palliate) symptoms in people with advanced cancer causing intestinal blockage, bleeding, or pain.

Types of radiation therapy

Different types of radiation therapy can be used to treat colon and rectal cancers.

External-beam radiation therapy: This is the type of radiation therapy most often used for people with colorectal cancer. The radiation is focused on the cancer from a machine outside the body.

Before treatments start, the radiation team takes careful measurements to determine the correct angles for aiming the radiation beams and the proper dose of radiation. External radiation therapy is much like getting an x-ray, but the radiation is more intense. The procedure itself is painless. Each treatment lasts only a few minutes, but the setup time -- getting you into place for treatment -- usually takes longer. Most often, radiation treatments are given 5 days a week for several weeks, but the length of time may be shorter if it is given before surgery.

Endocavitary radiation therapy: This type of treatment is used for some rectal cancers. A small device is placed through the anus and into the rectum to deliver high-intensity radiation over a few minutes. This is repeated about 3 more times at about 2-week intervals for the full dose. The advantage of this approach is that the radiation reaches the rectum without passing through the skin and other tissues of the abdomen, which means it is less likely to cause side effects. This can let some patients, particularly elderly patients, avoid major surgery and a colostomy. It is used only for small tumors. Sometimes external-beam radiation therapy is also given.

Brachytherapy (internal radiation therapy): Brachytherapy uses small pellets of radioactive material. These are put into a catheter or tube that was placed next to or directly into the cancer. The radiation travels only a short distance, limiting the effects on surrounding healthy tissues. It is sometimes used to treat people with rectal cancer, particularly people who are not healthy enough to tolerate curative surgery. This can be done a few times a week for a couple of weeks, but it can also be just a one-time procedure.

Radioembolization: Radiation can also be given during an embolization procedure. This was discussed in more detail in the section “Ablation and embolization to treat colorectal cancer.”

Side effects of radiation therapy

If you are going to get radiation therapy, it's important to speak with your doctor beforehand about the possible side effects so that you know what to expect. Potential side effects of radiation therapy for colon and rectal cancer can include:

  • Skin irritation at the site where radiation beams were aimed, which can range from redness to blistering and peeling
  • Nausea
  • Rectal irritation, which can cause diarrhea, painful bowel movements, or blood in the stool
  • Bowel incontinence (stool leakage)
  • Bladder irritation, which can cause problems like feeling like you have to go often (called frequency), burning or pain while urinating, or blood in the urine
  • Fatigue/tiredness
  • Sexual problems (impotence in men and vaginal irritation in women)

Most side effects should lessen after treatments are completed, but problems such as rectal and bladder irritation may not go away completely. If you begin to notice these or other side effects, talk to your doctor right away so steps can be taken to reduce or relieve them.

You can learn more about radiation treatments in the “Radiation Therapy” section of our website, or in our document Understanding Radiation Therapy: A Guide for Patients and Families.

Last Medical Review: 10/15/2014
Last Revised: 08/13/2015