Long term side effects of radiotherapy for rectal cancer

Most side effects gradually go away in the weeks or months after treatment. But some side effects can continue. Or you might notice some that begin months or years later.

Most of these side effects are rare. There are things you can do to deal with any effects that you have. 

Tiredness and weakness

Tiredness after radiotherapy might carry on for some months. You might also feel weak and lack energy. Various things can help you to reduce tiredness and cope with it, for example exercise.

Some research has shown that taking gentle exercise can give you more energy. It is important to balance exercise with resting.

Frequent or loose poo

Your bowel movements might be looser or more frequent than before your treatment.

You might need to take anti diarrhoea medicines, such as loperamide (Imodium). Bulking agents, such as Fybogel might also help. Your doctor or nurse can prescribe these for you, talk to your doctor before taking these.

You might find that you need to avoid high fibre foods. Although we normally think that a high fibre diet is the most healthy, it might make long term diarrhoea worse. Some people find it best to avoid high fibre vegetables, beans and pulses (such as lentils).

Let your doctor know if you have ongoing problems with frequent bowel movements or bleeding. They can refer you to a specialist team. The team includes cancer doctors, digestive system specialists, bowel surgeons, dietitians and specialist nurses.

Inflammation of the back passage (proctitis)

Inflammation of the back passage (rectum) is a long term side effect. Proctitis can cause a feeling of wanting to strain whether or not you actually need to pass a bowel movement. You might also have bleeding from your back passage or a slimy mucous discharge.

Bleeding is usually slight but can be more severe for some people. Talk to your radiographer or nurse if you have proctitis. They might suggest you use treatments such as steroid suppositories for a short time. This might reduce the inflammation. 

Bladder changes

Some people may have changes to the bladder, causing:

  • leaking of urine (bladder incontinence)
  • needing to pass urine more often due to the bladder wall becoming less stretchy
  • fragile blood vessels in the wall of your bladder that might cause blood in your urine
Speak to your doctor if you are worried about any symptoms.

Radar key and 'Just Can’t Wait' card

Many people worry about having access to a toilet when they’re out. There are special keys called radar keys. They give you access to thousands of toilets in the UK and their location.

You can also get a 'Just Can't Wait' card, this gives you peace of mind and access to toilets in a rush. 

Weaker pelvic bones

Radiotherapy can damage the bone cells in the pelvic area, and also lower the blood supply to the bones. The bones can become weaker. This is called avascular necrosis. Damage to the bones can cause pain and sometimes makes it hard to walk or climb stairs.

Your doctor will monitor you carefully, including checking your bone strength with a DEXA scan. They might suggest treatment with painkillers and walking aids to help you get around, such as a stick. You might also need to take medicines to strengthen the bones called bisphosphonates. These drugs can help to control pain and reduce the risk of fractures.

Tiny cracks in the bones

Sometimes, tiny cracks can appear in the pelvic bones some years after treatment. They are called pelvic insufficiency fractures. This is more likely to happen in people who have general weakening of their bones as they get older (osteoporosis). It is also more likely in people who are taking hormone therapies or steroids.

The pain, in this case, can be quite bad. It usually gets worse if you move around or do exercise and gets better when you sit still or rest. This type of pain normally goes away overnight. It doesn't stop you from sleeping well. Your doctor might ask you to have x-rays, a CT scan or an MRI scan (or a combination of these) to see if there are any fractures in the bones.

Changes to your sex life

You can have some changes that can affect your sex life. These changes may continue some time after treatment. 

Men can experience a lower sex drive, difficulty in getting an erection or problems with ejaculation.

Women may have dryness and shrinkage of the vagina, making sex painful. Some women also experience an early menopause.

Both men and women might lose their fertility.

Talk to your doctor if you think you have developed any of these side effects.

There are ways of reducing and managing them. Sometimes other conditions can cause similar symptoms to the long term side effects of rectal cancer radiotherapy.

Low levels of vitamin B12

You might have low levels of a vitamin B12 deficiency after radiotherapy to the pelvis (the area between your hip bones). This is called a vitamin B12 deficiency.

Radiotherapy can stop your digestive system taking in (absorbing) vitamin B12 from the food you eat. This is called malabsorption. This means you can have a B12 deficiency even if you eat a balanced diet.

A B12 deficiency can be a cause of anaemia. This can lead to a feeling of weakness, constipation or diarrhoea and numbness and tingling.

It’s important that you go to your doctor if you’re experiencing these symptoms so that they can help you.

Last reviewed: 
05 Mar 2022
Next review due: 
05 Mar 2025
  • Late patient-reported toxicity after preoperative radiotherapy or chemoradiotherapy in nonresectable rectal cancer: results from a randomized Phase III study
    M Brændengen and others
    International Journal Radiation Oncology Biology Physics, 2011. Volume 81, Pages 1017

  • Quantifying fatigue in (long-term) colorectal cancer survivors: a study from the population-based patient reported outcomes following initial treatment and long term evaluation of survivorship registry
    Thong and others
    European Journal of Cancer, 2013. Volume 49, Pages 1957

  • Sexual function in males after radiotherapy for rectal cancer
    K Bruheim and others
    International Journal Radiation Oncology Biology Physics, 2010. Volume 76, Page 1012

  • The holistic management of consequences of cancer treatment by a gastrointestinal and nutrition team: a financially viable approach to an enormous problem?
    A Muls and others
    Clin Med, 2016. Volume 16, Pages 240-246. 

  • Radiation Proctitis: Current Strategies in Management
    L Nhue and others
    Gastroenterol Res Pract, 2011. 

  • Insufficiency fracture after radiation therapy​
    O Dongryul and others
    Radiat Oncol J, 2014. Volume 32, Pages 213–220.

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