Side effects of radiotherapy

Side effects tend to start a week 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.

The side effects vary from person to person. You might 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.

The skin around your anus and back passage (rectum) is very sensitive. Radiotherapy can make it red and sore. 


  • Wash your skin with tepid water and simple soaps.
  • Pat your skin dry with a soft towel.
  • Ask your doctor, nurse or radiographer for creams to protect your skin and help it heal quickly.
  • Don't use perfumed or medicated soaps and lotions.
  • Try using a soft cushion if you have difficulty sitting comfortably for a while.

After your treatment is over, the soreness should gradually get better over a few weeks. 

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.

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

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.

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.  

Side effects if you have chemotherapy with radiotherapy

Chemotherapy combined with radiotherapy can make some side effects worse. Combining these treatments is called chemoradiotherapy.

Last reviewed: 
25 Oct 2018
  • Rectal cancer: ESMO Clinical Practical Guidelines for diagnosis, treatment and follow up
    R Glynne-Jones and others
    Annals of Oncology, 2017. Volume 28, Pages 422-440

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