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Radiation Therapy for Colon Cancer

What Do I Need to Know?


Updated March 05, 2012

Don't let the term "radiation therapy" scare you off. You will not "glow in the dark" after your treatment. Radiation therapy is an effective treatment for colon cancer, and commonly delivered as an adjuvant therapy (meaning it complements another treatment, such as surgery). Special, high-dose x-ray beams are used to kill rapidly dividing cells, like the colon cancer cells. Radiation therapy will also kill healthy cells, but they can rejuvenate.

Treatment by Colon Cancer Stage

The stage and grade of your colon cancer plays a large role in which treatment modalities are optimal. Radiation therapy is used to treat all stages of colon cancer, from stage 0 (carcinoma in situ) to stage IV (metastatic disease). Whether or not this treatment is appropriate for you depends on the location and size of your tumor, as well as your physical health, age, and the aggressiveness of your cancer (how likely it is to spread quickly).

Types of Radiation Therapy

Depending on your tumor size and location, your doctor may encourage radiation therapy before, during or after surgery. After all, bowel surgery remains the foremost treatment for most colon cancers –- but there is a catch. Sometimes, the colon tumor may be very close to, or adhering to, other organs or the lining in your abdomen. When that happens, your doctor may encourage you to have radiation therapy to kill those errant cancer cells.

  • External beam radiation -– administered using high dose, targeted x-rays. There are different approaches to the external beam radiation, including:
    1. Intensity Modulated Radiation Therapy (IMRT) -– The x-ray beam is shaped to fit your tumor.
    2. Image Guided Radiation Therapy (IGRT) –- A computed tomography (CT) scan or x-ray is used to pinpoint your tumor focus.
    3. Three Dimensional Conformal Radiation Therapy (3-D CRT) –- This uses a CT scan to view a three-dimensional image of the tumor prior to therapy.
  • Internal radiation therapy -- radioactive materials (seeds, wires) placed on or near the tumor.

  • Intraoperative -- during bowel surgery, radiation therapy is administered directly to the tumor either by external beam or internal means.

Radiation Before Surgery

Most common for rectal tumors, radiation is administered prior to surgical removal. The goal of radiation therapy is to shrink the tumors to a more manageable size for removal.

Radiation During Surgery

Also called "intraoperative radiation therapy," radiation can be administered during surgery directly to the organs surrounding the surgical site (liver, small intestine) or the abdominal lining for metastasis.

Radiation After Surgery

Radiation therapy can kill tricky cancer cells that may be left behind after the surgery. This does not mean your surgeon wasn’t amazing or the surgery was unsuccessful -– colon cancer cells are microscopic and your surgeon cannot see them.

Your Radiation Professionals

Radiation therapy is ordered and administered by a specialized doctor called a radiation oncologist. He or she may work alongside radiation nurses, therapists and even a physicist to maximize your treatment potential and care for you during treatments.

The Doctor Ordered Radiation Therapy, Now What?

First, you will meet with your radiation oncologist. He or she will review your medical history, physical exam and prior testing and treatment (if applicable) results. The doctor will discuss his or her goals for the radiation treatment. Although radiation therapy can meet many different end goals, there are three common goals to treatment:

  • Shrink the tumor prior to surgical removal
  • Cure the cancer by killing off cancerous cells
  • Reduce uncomfortable symptoms (abdominal pain, constipation) related to the tumor’s presence

The radiation oncologist and physicist will work together to find the best method of delivering the radiation to your tumor (internal versus external). Treatments are usually administered over a short time frame, such as six weeks, where you will go to the outpatient center or clinic for daily radiation treatments. You may have one or two breaks during the week, which allow your healthy cells to rejuvenate and the dead cancer cells to get filtered out of your body.

If you elect external beam radiation therapy, your first appointment will not consist of any actual radiation therapy. This appointment is referred to as the "mapping" appointment, during which the radiation oncologist uses x-ray beams or CT scans to pinpoint (map) the location of your tumor. You will probably get one or more tiny tattoos (think the tip of a pen) on your skin to mark the exact location where the external beam of radiation is to be focused.

Similar to chemotherapy, radiation therapy carries a risk of uncomfortable side effects. Because this form of treatment kills both healthy and cancerous cells, the side effects are directly related to the death of healthy cells and may include:

  • Nausea, vomiting, or diarrhea
  • Urinary difficulties
  • Decreased blood count
  • Mouth sores
  • Skin rash (groin or by beam focus area)
  • Feeling tired

Talk to your doctor and nurses if any of these symptoms are present. The medical staff works daily with patients and are trained to help you mitigate these disturbing side effects, allowing you to finish your therapy with minimal discomfort.


American Cancer Society. (2006). American Cancer Society’s Complete Guide to Colorectal Cancer. Clifton Fields, NE: American Cancer Society.

American Cancer Society. (n.d.). Radiation Treatment for Colon and Rectal Cancer. Accessed February 25, 2012.

National Cancer Institute. (n.d.). Rectal Cancer Treatment. Accessed February 27, 2012.

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