Radiation therapy for colorectal cancer

This page was reviewed under our medical and editorial policy by

Maurie Markman, MD, President, Medicine & Science

This page was reviewed on June 9, 2022.

Treatment for colorectal cancer may involve various steps. In addition to surgery and powerful drugs such as chemotherapy, radiation therapy may be a recommended part of a personalized care plan.

In general, radiation therapy uses high-energy X-rays to kill cancer cells. In the treatment of colorectal cancer, it’s more widely used in cases of rectal cancer than colon cancer. Sometimes, chemotherapy is given at the same time as radiation therapy (a process called chemoradiation) in order to make the radiation therapy work better.

When is radiation therapy used to treat colorectal cancer?

Although used less often for colon cancer than rectal cancer, radiation therapy for colorectal cancer may be an option:

  • Before surgery, possibly in conjunction with chemotherapy, to make the tumor smaller and easier to remove (most often for rectal cancer)
  • During surgery to help destroy any remaining cancer cells (intraoperative radiation therapy, or IORT)
  • After surgery to help destroy remaining cancer cells
  • To help control painful symptoms caused by advanced colorectal cancer
  • To help control the cancer if surgery isn’t an option
  • To treat a cancer recurrence
  • To treat cancer that has metastasized or spread beyond the colon or rectum

How is radiation therapy administered for colorectal cancer?

Radiation therapy is delivered in a few different ways, depending on the specific source of the radiation.

External beam radiation therapy (EBRT)

External beam radiation therapy is radiation delivered externally by a machine. It’s the most common type of radiation therapy for colorectal cancer. During this treatment, radiation is delivered from a machine aimed at the part of the body where the cancer was detected, similar to how an X-ray is performed (although EBRT is more powerful).

When targeting cancer that has spread, newer forms of EBRT may be used, delivering more precise treatments that are designed to expose less nearby healthy tissue to the radiation. These technologies include 3D conformal radiation therapy, intensity modulated radiation therapy and stereotactic body radiation therapy.

Internal radiation therapy (IRT)

In some cases, the care team may use internal radiation therapy to deliver a concentrated dose of radiation directly to cancer cells using a process called brachytherapy. This type of radiation therapy places radioactive material inside the body. For rectal cancer, this treatment involves placing a radioactive source within or right next to the tumor. Ways to deliver the radiation include endocavitary radiation, which uses a device that looks like a balloon, and interstitial brachytherapy, which delivers radiation to the tumor from a radioactive pellet.

Interventional radiology

Interventional radiology uses minimally invasive techniques to target cancer cells. One form of interventional radiology is radioembolization. This form of treatment is used for colorectal cancer that’s spread to the liver. It involves injecting small beads coated with radioactive material into the hepatic artery in the liver. The beads give off radiation that targets cancer in the liver.

How long does it take to administer radiation therapy for colorectal cancer?

The length of radiation treatments varies depending on the radiation technique used. For instance, with EBRT, the patient may receive radiation therapy for a few days or weeks. The most common schedule for endocavitary radiation therapy is four treatments lasting just minutes each and given at two-week intervals. Interstitial brachytherapy may be administered just once or a couple of times a week over a few weeks.

The type of colorectal cancer also determines the length of time the patient will have radiation therapy. For example, when it’s given prior to surgery for rectal cancer, it may be started five or six weeks in advance of the surgery date.

Patients should talk to their care teams to get a better understanding of how long a radiation therapy regimen may last.

Side effects of radiation therapy for colorectal cancer

As with other cancer treatments, radiation therapy may cause side effects. Most go away when colorectal cancer treatment stops, but some may continue. Possible side effects include:

  • Bloody stools
  • Burning or pain while urinating
  • Diarrhea
  • Fatigue
  • Feeling like you have to urinate often
  • Leakage of stool
  • Nausea
  • Painful bowel movements
  • Red, blistering or peeling skin where the radiation beams were used
  • Vaginal irritation for women
  • Sexual challenges in men and women

Sexual challenges may include infertility when radiation therapy is delivered to the pelvic region. Patients should talk to their care teams in advance to learn more about how radiation therapy could affect sexual health and what options may help preserve their fertility.

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