Radiation Therapy for Colorectal Cancer

Radiation therapy uses high-energy X-rays, electron beams, or chemical agents called radioactive isotopes to attack cancer. The radiation is aimed directly at the tumor. It damages chromosomes in cancer cells so they can't multiply.

As a treatment for colorectal cancer, it can help control the disease and help some people live longer.

If you have rectal cancer, meaning the tumor started in your rectum, your doctor may use radiation either before or after surgery. It's often used with chemotherapy. If surgery isn't an option for you, it can be used alone to help with pain, bleeding, or blockages.

If you have colon cancer, meaning the cancer began in your large intestine, you may have radiation after surgery. It can help kill any cancer cells that may have been left behind. It also can be used alone if you don't have surgery.

Types of Radiation Treatments

Among other things, your doctor will consider the type, location, and size of your cancer when deciding which kind of radiation therapy -- internal or external -- is right for you.

External Beam Radiation Therapy

This is the most common form for people with colorectal cancer. A machine is used to aim a beam of radiation at your tumor. It's painless.

Before treatment begins, a team of specialists, including a radiation oncologist, will use measurements from scans to find the exact spot to aim the radiation. They'll tattoo small dots on your body to show where to target the beam. This ensures they get the same location at every treatment.

You'll sit or lie on a table so a beam from a machine can be aimed at the tumor. You'll need to be still, but it lasts only a few minutes. You may have five treatments a week for several weeks, and sometimes, you'll be treated a few times a day for several weeks.

There are many types of external beam radiation. These include 2D, 3D conformal, IMRT, IGRT, and proton beam therapy.

Internal Radiation Therapy

Interstitial radiation therapy (also known as brachytherapy) uses a tube to place small pellets, or seeds, of radioactive material directly into your tumor. After 15 minutes, they're taken out. You may have up to two treatments a week for 2 weeks.

Endocavitary radiation therapy is often used for rectal cancer. A device called a proctoscope is placed in your anus to carry radiation directly to the tumor. It stays there a few minutes and then is taken out. You'll probably have four treatments, each about 2 weeks apart.


What Are the Side Effects of Radiation Therapy?

Side effects tend to be specific to the area of your body that gets the radiation. Talk to your doctor about what you can expect.

You may have:

  • Blood in your stool
  • Lack of energy
  • Leaky bowels
  • Pain and burning on your skin where beams were aimed
  • Pain during bowel movements
  • Pain when you pee
  • Problems having sex

Most side effects should get better a few weeks after treatment ends, but some may not go away. Medications and other treatments can help. Discuss any side effects with your doctor so he can help you with them.

WebMD Medical Reference Reviewed by Laura J. Martin, MD on October 28, 2018



American Cancer Society: "Radiation therapy for colorectal cancer."

Cancer.Net: "Colorectal Cancer -- Treatment Options."

Deisler, D. Clinical Colorectal Surgery Journal, Aug 2007.

John Hopkins Medicine: "Brachytherapy."

Cancer Research UK: "Side effects of bowel cancer radiotherapy."

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