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Colorectal Cancer: Radiation Therapy

What is radiation therapy?

Radiation therapy uses high-energy radiation from X-rays to kill cancer cells.

When might radiation therapy be used?

Radiation therapy is a major part of the treatment for rectal cancers. It’s also sometimes used as a treatment for colon cancers. There are several reasons your healthcare provider may recommend this therapy:

  • To try to shrink a tumor before surgery for rectal cancer. This may make the tumor easier to remove. And it might reduce the amount of surgery needed.

  • To try to kill any cancer cells left after surgery.  For colon cancer, this may be use if surgery was done to remove a cancer that was attached to an organ or to the lining of your abdomen, but the surgeon isn’t sure all the cancer cells were removed. 

  • To ease symptoms caused by tumors that can't be treated with surgery or that have spread to other organs.

Radiation therapy is not a substitute for surgery. Surgery is generally the main treatment for colorectal cancer, except in cases of advanced cancers that can’t be removed with surgery, or in people who are not healthy enough to have surgery.

To plan your entire treatment strategy, consult with a team of cancer specialists. This might include a surgeon, radiation oncologist, and medical oncologist.

What happens during radiation therapy

For colorectal cancer, the most common way to receive radiation is from a machine outside your body that gives off an invisible X-ray beam. This is called external radiation. In some cases for rectal cancer, a radioactive source is put right into or next to the tumor, where it gives off radiation for a short time. This is known as internal radiation.

A specialist called a radiation oncologist creates your treatment plan. The plan shows what kind of radiation you’ll have and how long the treatment will last. If you need radiation combined with chemotherapy, you’ll also see another doctor called a medical oncologist.

You will have external radiation therapy in a hospital or a clinic. You will likely be an outpatient. That means you will go home the same day. External radiation is typically given 5 days a week for several weeks. If you also have chemotherapy, you will receive it in a different outpatient area.

Preparing for radiation

Before your first treatment, you’ll have an appointment to plan for the treatment. This is called simulation. During this appointment:

  • You may be given barium, a liquid that allows your doctor to see where your colon is on an X-ray image. You’ll drink some of the barium, and some will be put in your rectum.

  • You’ll lie on a table while a radiation therapist uses a machine to find exactly where the radiation will be aimed.

  • The therapist may mark your skin with tiny ink dots. These are used to aim the radiation at the exact same place each time.

  • You may have other imaging tests, such as CT scans, to help locate the tumor.

  • You may have body molds made to keep you from moving during the treatment.

On the days you get radiation

Radiation treatment is like getting an X-ray, although the radiation is stronger.

On the days you have treatment, you’ll lie on a table. A radiation therapist may place blocks or special shields to protect healthy parts of your body. The therapist then lines up the machine. You may see lights from the machine lined up with the marks on your skin. These help the therapist know you are in the right position. The therapist will leave the room while the machine sends radiation to your tumor. During this time the therapist can see you, hear you, and talk to you.

You can’t feel radiation, so the process will be painless. Also, you will not be radioactive afterward.

What to expect after radiation therapy

Radiation therapy affects normal cells, as well as cancer cells. This can cause side effects. The side effects depend on the amount and type of radiation. Some people have few or no side effects. But if you have them, your doctor may change the dose of your radiation or how often you have treatments. Or the doctor may stop treatment until the side effects go away. Talk with your doctor about any side effects you have.

Possible short-term side effects

These are some of the common short-term side effects:

  • Diarrhea

  • Nausea

  • Bladder irritation

  • Feeling the need to urinate often

  • Pain or burning feeling when you urinate

  • Feeling very tired

  • Low blood counts, as noted from a blood test

  • Skin irritation or changes in areas that get radiation

Some of these side effects can be controlled with medicine, and some may be helped with diet. Talk with your doctor or nurse about how to deal with them and how to know when they become serious. Often these side effects go away a few weeks after you stop treatment.

Possible long-term side effects

Radiation therapy can cause some long-term side effects, depending on where the radiation was aimed. These can be more serious, so you should watch them closely with your doctor:

  • Bowel or bladder irritation. You may feel the need to urinate or have bowel movements more often. You may also have some pain with urination or bowel movements, or see blood in your urine or stool. Be sure your doctor is aware of these problems so that they can be treated, if needed.

  • Early menopause. If you're a woman who hasn’t gone through menopause, you may have menopausal symptoms. Talk with your doctor about what you can do to ease the symptoms.

  • Vaginal dryness. Women may have vaginal dryness and narrowing. Both conditions may be permanent. Lubricants can help with vaginal dryness. Vaginal narrowing may be helped by using a vaginal dilator or by having sexual intercourse.

  • Decreased sperm count. Men may produce less ejaculate, and their semen may have a lower sperm count. If you're planning on having children, you may want to discuss using a sperm bank before having your radiation treatments. 

Online Medical Reviewer: Alteri, Rick, MD
Online Medical Reviewer: Knoble, Jeanna, MD
Last Review Date: 11/1/2015
© 2013 The StayWell Company, LLC. 800 Township Line Road, Yardley, PA 19067. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare provider's instructions.