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Radiation Therapy for Colorectal Cancer

Radiation therapy uses high energy x-rays to kill cancer cells. Radiation is tailored for each person. This helps to deliver as much radiatoin as possible to cancer cells and decrease harm to healthy cells. Radiation therapy is often used along with other treatments, such as surgery and chemotherapy. It may be used to clear any cancer cells left after surgery. Some may need it if they cannot have surgery, but this is rare.

Types of radiation therapy used for colorectal cancer are:

External Beam Radiation

Short bursts of x-rays are fired from a machine toward the cancer. Special blocks are used to shape the radiation beam. Marks are also made on the body. These steps help to focus the beam. It will help to treat the cancer and harm as little normal tissue as possible.

Radiation of a Tumor

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Side Effects and Management

Radiation to the belly and pelvis may cause:

  • Anal and/or rectal irritation causing:
    • Blood in the stool
    • Pain during bowel movements
    • Leaking stool
  • Bladder irritation causing:
    • Pain or burning during urination
    • Blood in the urine
  • Men may have problems getting and keeping an erection
  • Women may have vaginal dryness and discomfort during sex
  • Infertility

Other treatments can help to ease side effects. It can help treat dry, irritated skin, nausea, vomiting, or diarrhea. Radiation treatment can also affect some blood cells. This can lead to anemia and fatigue. Medicine can help to improve blood cells. Early treatment of side effects may have best outcome.


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Kuipers EJ, Grady WM, Lieberman D, et al. Colorectal cancer. Nat Rev Dis Primers. 2015 Nov 5;1:15065

Rectal cancer treatment option overview. National Cancer Institute website. Available at: Updated October 2, 2019. Accessed December 4, 2019.

Last reviewed December 2019 by Mohei Abouzied, MD  Last Updated: 12/2/2019