Radiation therapy for anal cancer

Radiation therapy uses high-energy rays or particles to destroy cancer cells. Most people with anal cancer have radiation therapy. It is usually given during the same time period as chemotherapy. This is called chemoradiation.

Your healthcare team will consider your personal needs to plan the type and amount of radiation, and when and how it is given. You may also receive other treatments.

Radiation therapy is given for different reasons. You may have radiation therapy to:

  • destroy the cancer cells in the body
  • treat any cancer that remains after other treatments (called salvage therapy)
  • treat cancer that comes back, or recurs
  • relieve pain or control the symptoms of advanced anal cancer (called palliative therapy)

Types of radiation therapy

The following types of radiation therapy are most commonly used to treat anal cancer.

External beam radiation therapy

During external beam radiation therapy, a machine directs radiation through the skin to the tumour and some of the tissue around it, including lymph nodes. It is usually given as part of chemoradiation to treat anal cancer.

Conformal radiation therapy is a specialized type of external beam radiation therapy. It allows doctors to accurately target the area to be treated. This means that the normal tissue around the tumour won’t be damaged by the radiation. The types of conformal radiation therapy that may be used for anal cancer are intensity-modulated radiation therapy (IMRT) or 3-D conformal radiation therapy (3-D CRT). They usually cause less severe side effects than other types of external beam radiation therapy.

External beam radiation therapy is usually given once a day, 5 days a week, for 5–6 weeks. An extra boost of radiation may be given if treatment with chemoradiation didn’t destroy all the cancer cells, the tumour is large or cancer has spread to lymph nodes. A boost of radiation is not needed when IMRT is used.


Brachytherapy is internal radiation therapy. It uses a radioactive material called a radioactive isotope. It is placed right into, or very close to, the tumour. Radioactive materials can also be placed in the area from where the tumour was removed. The radiation kills the cancer cells over time.

Brachytherapy may be used after external beam radiation therapy to give a boost of higher-dose radiation to the tumour and area around the tumour.

Radiation oncologists need special equipment to give brachytherapy. As a result, it isn’t available in all treatment centres and it isn’t a standard treatment for anal cancer.

Side effects

Side effects can happen with any type of treatment for anal cancer, but everyone’s experience is different. Some people have many side effects. Other people have few or none at all.

During radiation therapy, the healthcare team protects healthy cells in the treatment area as much as possible. But damage to healthy cells can happen and may cause side effects. Side effects can happen any time during, immediately after or a few days or weeks after radiation therapy. Sometimes late side effects develop months or years after radiation therapy. Most side effects go away on their own or can be treated, but some side effects may last a long time or become permanent.

Side effects of radiation therapy will depend mainly on the size of the area being treated, the specific area or organs being treated, the total dose of radiation and the treatment schedule. Some common side effects of radiation therapy used for anal cancer are:

Tell your healthcare team if you have these side effects or others you think might be from radiation therapy. The sooner you tell them of any problems, the sooner they can suggest ways to help you deal with them.

Questions to ask about radiation therapy

Find out more about radiation therapy and side effects of radiation therapy. To make the decisions that are right for you, ask your healthcare team questions about radiation therapy.

Expert review and references