Bowel changes after pelvic radiotherapy

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The bowel is made up of the small bowel and the large bowel. Sometimes, pelvic radiotherapy can cause changes to the way the bowel works. In some people, these changes will not get better after treatment finishes. Others may not develop until months or years after treatment has finished.

Pelvic radiotherapy can cause scarring (fibrosis) in the lining of the large bowel which can mean solid waste passes through quickly. The muscles that help to hold stool in the rectum may also be weakened. Sometimes, pelvic radiotherapy causes the small blood vessels in the bowel to become more fragile and may cause the bowel to narrow. These changes lead to symptom such as diarrhoea, constipation, leaking (incontinence) or bleeding from the back passage (bottom).

Many bowel problems can be managed or treated successfully. Tell your doctor about any symptoms you are having. They can give you advice and may do some tests. They may also refer you to see a bowel specialist (a gastroenterologist).

Changes to the bowel

Sometimes, people who have had pelvic radiotherapy have changes in the way their bowel works. For some people, these changes start during treatment and don’t get better. But for others, the changes may develop months or years after treatment.

The bowel is part of the digestive system. It is made up of the small bowel and the large bowel. The small bowel absorbs nutrients from the food we eat. It then passes the liquid waste into the large bowel (colon and rectum). The colon absorbs water from the waste before passing the more solid waste (faeces or stool) into the rectum. The stool is held in the rectum until it’s ready to be passed through the opening to the outside of the body (anus).

Possible late effects to the bowel

Radiotherapy can affect the blood supply to the bowel. This makes the bowel tissue and the small blood vessels in it more fragile. It may cause bleeding from the back passage.

Radiotherapy can also cause scarring (fibrosis) in the large bowel lining, making it thicker and less flexible. This causes solid waste to pass through more quickly than before, so nutrients may not be as well absorbed. The bowel will also be unable to hold as much solid waste (stool).

The muscles that help hold stool in the rectum can also be affected, which may cause problems with bowel control and leakage (incontinence).

Radiotherapy can also make the bowel narrow. When radiotherapy affects the small bowel, it can cause food intolerance, or conditions such as bile acid malabsorption or small bowel bacterial overgrowth.


The symptoms of late effects to the bowel can include:

  • bleeding from the back passage
  • passing mucus (a clear, sticky substance)
  • cramps or spasms in the bowel, which may be painful
  • feeling that you haven’t emptied your bowel completely (tenesmus)
  • diarrhoea or severe constipation
  • needing to rush to open your bowels (urgency)
  • leakage or soiling (incontinence)
  • passing a lot of wind.

Some people find their symptoms don’t cause too many problems, and they can manage them fairly easily. The change in the way the bowel works may be small, for example having to go to the toilet twice a day instead of once. But sometimes bowel changes can have a much bigger impact and interfere with day-to-day life.

Talking to your doctor

There are lots of ways of managing or treating your symptoms. Your doctor can advise you, or they may need to refer you to:

  • a specialist in bowel problems (a gastroenterologist)
  • a specialist nurse or physiotherapist who gives advice on incontinence and treatment (a continence adviser).

There are three problems you must always talk to your doctor about:

  • Passing blood from your back passage.
  • Waking up from sleep to open your bowels.
  • Needing to rush to open your bowels, or having accidents.

These symptoms may not be due to anything serious, but you should always get them checked out. They can often be treated simply. Occasionally they can be a sign of a more serious problem, so it is important to find out the cause as soon as possible.


You may have tests to find out what’s causing your symptoms. Tests can include:

  • blood and stool tests
  • x-rays and scans
  • an endoscopy – this is where a doctor or nurse passes a thin tube with a light on the end (an endoscope) into the bowel to look for any abnormal areas.

Some people may need to have a sample of tissue removed (a biopsy) from the bowel. This will be done by an experienced bowel specialist.

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