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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. Radiation therapy is not a substitute for surgery. Surgery is often the main treatment for colorectal cancer. But some cases of advanced cancer can’t be removed with surgery. Or some people are not healthy enough to have surgery. There are several reasons your healthcare provider may advise 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, it may be used if a cancer growth was attached to an organ or to the lining of your abdomen. In these cases, the surgeon may not be sure all the cancer cells were removed. 

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

To plan your treatment strategy, you will talk with a team of cancer specialists. 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.

What happens during radiation therapy?

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

You may 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 often given 5 days a week for several weeks. If you also have chemotherapy, you will have it in a different outpatient area.

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 the simulation:

  • You may be ask to drink a cup of a contrast agent such as barium. This is a liquid that allows your doctor to see your colon is on a CT scan or X-ray image. You’ll drink some of the barium. Some may also be put in your rectum with a soft, small rubber tube. In some cases, your doctor may ask you to drink liquid contrast agent the day before your procedure.

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

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

  • You may have other imaging tests to help locate the tumor. These may include a CT scan.

  • You may have body molds made to help you stay in the same position each day during treatment.

On the days you get radiation

Radiation treatment is like getting an X-ray. The radiation is stronger so it can kill cancer cells. You can’t feel radiation, so the process will be painless. Also, you will not be radioactive afterward.

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 and laser lines projected from the machine lined up with the marks on your skin. These help the therapist know you are in the right position. The radiation machine may be used to take X-rays or CT-scans before treatment. This is done to help with alignment. 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. The treatment itself usually takes only a few minutes.

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 your doctor may stop treatment until your side effects go away. Talk with your healthcare team about any side effects you have.

Possible short-term side effects

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

  • Diarrhea

  • Gas and bloating

  • 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 skin changes in areas that get radiation

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

Possible long-term side effects

Radiation therapy can cause some long-term side effects. This depends on where the radiation was aimed. These can be more serious, so you should watch them closely and talk with your healthcare team. The long-term side effects can include:

  • 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 (hormone changes) or infertility (inability to become pregnant). 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. This can lead to painful intercourse or bleeding.  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.

  • Lower sperm count. Men may produce less semen. Their semen may have a lower sperm count. This could lower a man's fertility. But it might still be possible to get a woman pregnant. If you're planning on having children, you may want to discuss using a sperm bank before having your radiation treatments. 

  • Erectile dysfunction. Men may have trouble getting or keeping erections. This condition may be improved with medicines or a penile pump.

Online Medical Reviewer: Alteri, Rick, MD
Online Medical Reviewer: Herold, David M., MD
Date Last Reviewed: 12/1/2017
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