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Radiation therapy is treatment with high energy rays (like x-rays) to kill cancer cells or shrink tumors. Radiation can be used:

  • As part of the main treatment (along with chemotherapy) for most anal cancers
  • After surgery if the doctor is concerned that some of the cancer might not have been removed
  • To help treat cancer that has come back in the lymph nodes after treatment
  • To help control advanced cancer or to relieve symptoms it causes

There are 2 main forms of radiation therapy: external beam and internal radiation (brachytherapy).

External radiation

This is the most common way to give radiation for anal cancer. It uses a focused beam of radiation from a machine outside the body. Treatment is often given 5 days a week for about 5 weeks. Each treatment is much like getting a normal x-ray, but the radiation is stronger. The treatment itself lasts only a few minutes, although the setup time – getting you into place for treatment – usually takes longer.

Doctors often use newer techniques that let them give higher doses of radiation to the cancer while reducing the radiation to nearby healthy tissues.

Side effects

There can be side effects from radiation treatment. These vary based on the part of the body treated and the dose of radiation given.

Some common short-term side effects include:

  • Skin changes (like a sunburn) in areas being treated
  • Temporary anal swelling and pain
  • Discomfort during bowel movements
  • Feeling tired
  • Nausea
  • Diarrhea

In women, radiation can irritate the vagina. This can lead to discomfort and vaginal discharge.

These side effects often improve after radiation stops.

Long-term side effects can also occur:

  • Damage to anus can cause scar tissue to form. This can sometimes keep the anal sphincter from working as it should, which could lead to problems with bowel movements.
  • Radiation can weaken the bones of the pelvis or hip, increasing the risk of fractures.
  • Radiation can damage blood vessels that nourish the lining of the rectum, which can lead to the lining of the rectum becoming inflamed (chronic radiation proctitis). This can cause long-term rectal bleeding and pain.
  • Radiation can affect fertility (the ability to have children) in both women and men. (See our documents Fertility and Men With Cancer and Fertility and Women With Cancer.)
  • In women, radiation can lead to vaginal dryness and even a narrowing or shortening of the vagina, which can make sex painful. (See our document Sexuality for the Woman With Cancer.)
  • Radiation to the lymph nodes in the groin can cause swelling in the legs, called lymphedema. (For more, see our document Understanding Lymphedema: For Cancers Other Than Breast Cancer.)

Internal radiation (brachytherapy)

In this treatment, small sources of radiation are put inside the body, in or near the tumor. This can be done using permanent radioactive pellets, or “seeds,” which stay in the body and release their dose slowly over time, or with other techniques where the radioactive source is placed in the body for only a brief period. Fewer trips to the doctor are needed with this treatment.

This approach is used less often than external radiation. When it is used, it is usually given along with external radiation. The possible side effects are often like those seen with external radiation.

For more on radiation as a treatment for cancer, see the Radiation Therapy section of our website, or our document Understanding Radiation Therapy: A Guide for Patients and Families.

Last Medical Review: 06/10/2014
Last Revised: 01/20/2016