Radiation Therapy for Colorectal Cancer
by Jondavid Pollock, MD, PhD
Radiation therapy uses high energy x-rays to destroy cancer cells. A radiation oncologist will customize the treatment dose for individual needs. The goal is to try and kill as much cancer as possible while minimizing harm to healthy tissue. Radiation therapy is generally most effective when used in combination with other treatments, such as surgery and chemotherapy. It may be used to destroy remaining cancer cells after surgery, or rarely, as an alternative for people who cannot tolerate surgery.
Types of radiation therapy used for colorectal cancer:
External Beam Radiation
In external beam radiation therapy, radiation is produced by a machine called a linear accelerator. Short bursts of x-rays are fired from the machine at the cancer. The x-rays come out in a square-shaped manner. The radiation oncologist designs special blocks to shape the radiation beam so that it treats the cancer and as little normal tissue as possible.
Endocavitary radiation therapy is used to treat some rectal cancers. A high-intensity dose of radiation is delivered through the anus and into the rectum. This may cause fewer side effects because endocavitary radiation spares the skin and other abdominal tissue. It may also be used in combination with external beam radiation.
This is also called internal radiation therapy. Small pellets with radioactive material are placed near the cancer. Since radiation does not travel far from the pellets, it is less damaging to normal tissue. Brachytherapy is sometimes used in rectal cancer treatment.
Side Effects and Management
Complications of radiation therapy to the abdominal and pelvic areas may include:
A variety of treatments are available to help manage side effects of radiation therapy, such as dry, irritated skin, nausea, vomiting, diarrhea, and fatigue due to anemia. Sometimes adjustments to treatment doses may also be possible. The earlier side effects are addressed, the more likely they will be controlled with a minimum of discomfort.
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Accessed January 3, 2017.
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Colorectal cancer. Merck Manual Professional Version website. Available at:
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Updated July 2014. Accessed January 3, 2017.
Rectal cancer treatment option overview. National Cancer Institute website. Available at: https://www.cancer.gov/types/colorectal/patient/rectal-treatment-pdq#section/_135. Updated June 30, 2016. Accessed January 3, 2017.
Last reviewed December 2016 by Mohei Abouzied, MD
Last Updated: 12/4/2015
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