Side effects start about a week after the radiotherapy begins. They slowly get worse during treatment and a couple of weeks after treatment ends. They tend to begin to improve after around 2 weeks.
This page is about the side effects when you have radiotherapy as your main treatment for bladder cancer. Doctors sometimes call this radical radiotherapy.
Side effects of radiotherapy
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. Some research has shown that taking gentle exercise can give you more energy. Ask your healthcare team for advice about exercise in your situation. It's important to balance exercise with resting.
Your skin might go red or darker in the treatment area. You might also get slight redness or darkening on the other side of your body. This is where the radiotherapy beams leave the body. It's not likely to be that noticeable for bladder cancer but do tell your radiographer if you notice any skin changes.
The red or darker areas can feel sore. Using a cream helps keep the skin hydrated and soothe it. The soreness usually goes away within 2 to 4 weeks of ending the treatment. But your skin might always be slightly darker in that area.
Your radiographers will tell you which cream you should use.
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 or stinging pain when you do pass urine
You should try to drink more fluids than you would normally. Drinking tea and coffee doesn’t count, as they make you go to the toilet and do not hydrate you.
Many people think drinking cranberry juice can be helpful with bladder problems. But cranberry juice can increase the effects of warfarin (a blood thinner or anticoagulant). You should not drink cranberry juice if you are taking warfarin.
It's quite common to have a tube into your bladder (catheter) to help you pass urine during your radiotherapy treatment.
Your bladder inflammation should settle down after the treatment is over.
Tell your doctor if you have any pain when passing urine. It could be a sign that you have an infection. You may need antibiotic treatment.
Radiotherapy can inflame the lining of your bowel. This can cause diarrhoea. You may also have:
griping or cramping pain
an increase in wind
feeling you need to go to the toilet urgently
some mucus or blood in your poo (stool)
It’s important to drink plenty if you have diarrhoea, so you don't become dehydrated. Your doctor might prescribe tablets to help slow down your bowel if you need them. This should help to reduce the number of times you have diarrhoea. Changing your diet might also help lessen the number of times you need to go, such as reducing the amount of fibre if you have been following a diet very high in fibre. Ask your nurse or doctor about this.
Ask your nurse or radiographer for soothing creams to apply around your back passage (anus). The skin in that area can get very sore and might break if you have severe diarrhoea.
Diarrhoea should gradually get better a few weeks after your treatment has finished. Let your doctor or nurse know if it continues.
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.
Radiotherapy consent form for bladder cancer
The Royal College of Radiologists, 2025
Clinical Oncology: Basic principles and practice (5th edition)
Peter Hoskin
CRC Press, 2020
Quality of Life after Bladder Cancer: A Prospective Study Comparing patient- related Outcomes after Radical Surgery or Radical Radiotherapy for Bladder Cancer
A D Nikapota and others
Clinical Oncology, 2016. Volume 28, Issue 6, Pages 373 – 375
