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Side effects of external radiotherapy

Radiotherapy to the prostate can cause some side effects, such as loose or watery poo (diarrhoea) and passing wee (urine) more often.  

Side effects tend to start a week or 2 after the radiotherapy begins. They gradually get worse during the treatment and for a couple of weeks after the treatment ends. But they usually begin to improve after around 2 weeks or so.

These side effects vary from person to person. You may not have all of the effects mentioned.

Side effects can include:

You might feel tired during your treatment. It tends to get worse as the treatment goes on. You might also feel weak and lack energy. Rest when you need to.

Tiredness can carry on for some weeks after the treatment has ended but it usually improves gradually.

Various things can help you to reduce tiredness and cope with it, such as exercise. Some research has shown that taking gentle exercise can give you more energy. It's important to balance exercise with resting.

Your skin in the treatment area might get sore, or redden or darken. Following these tips can help with this: 

  • Wear loose fitting underwear and clothes. Natural fibres can be more comfortable than man-made fibres.
  • Gently wash the area each day. Use mild, unperfumed soap and warm or cool water. Try baby soap or liquid baby wash but check with the radiotherapy staff first.
  • Gently pat the skin dry with a soft towel. Rubbing the skin can make it sore.
  • Don't use perfumed lotions on the area. Use only creams or dressings recommended by your specialist or radiographer.
  • Don't use talcum powder because it can contain tiny metal particles. The particles can make the soreness worse.
Tell the nurse or radiographer at your treatment centre if you notice reddening or soreness. They can prescribe creams to help.

Radiotherapy causes hair loss in the treatment area. Sometimes the hair loss is patchy, rather than complete. The hair can grow back, but not always fully. It might take several months.

You may feel:  

  • as if you want to pass urine all the time (but when you go, there isn't much there)
  • as if you have a bladder infection (cystitis)
  • a burning pain when you do pass urine
  • a weak flow of urine 

Try to drink plenty of water. Many people think that drinking cranberry juice can be helpful with bladder problems. But this isn't the case for bladder problems caused by radiation. 

Your bladder inflammation should settle down a few weeks after your treatment is over.  

Tell your doctor if you have any pain when passing urine. It could be a sign that you have an infection. They might arrange for you to do a urine test (Mid Stream Urine). You may need antibiotic treatment.

Tell your doctor, nurse or radiographer if you have diarrhoea. They can prescribe medicine to help you. 

Drink at least 2.5 litres of fluid a day. This helps to keep you hydrated. If you struggle with this just try to drink as much as possible.

Ask your nurse about soothing creams to apply around your back passage (rectum). The skin in that area can get very sore and even break if you have severe diarrhoea.

Possible long term side effects

Most side effects gradually go away in the weeks or months after treatment. But some side effects can continue or might start some months or years later.  

Last reviewed: 
21 Jun 2019
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    National Institute for Health and Care Excellence (NICE), January 2014

  • EAU guidelines on prostate cancer. part 1: screening, diagnosis, and local treatment with curative intent-update 2013
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  • Multi-disciplinary Team (MDT) Guidance for Managing Prostate Cancer
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    CA: A Cancer Journal for Clinicians, 2008. Volume 58, Pages 196-213

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    SP Elliott, B Malaeb.
    World Journal of Urology, 2011. Volume 29, Pages 35-41

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