Externa beam radiotherapy for prostate cancer
Radiotherapy to the prostate can cause some side effects. These include loose or watery poo (diarrhoea) and problems passing urine.
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 after treatment finishes
Everyone is different and the side effects vary from person to person. You may not have all of the effects mentioned.
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. This can vary depending on your skin tone. 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.
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 need to pass urine as soon as possible (urgently)
as if you have a bladder infection (cystitis)
a burning pain when you do pass urine
a weak flow of urine
unable to pass urine
Try to drink plenty of water and avoid caffeine. 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.
Your doctor may prescribe you some medicine if the flow of urine slows down too much. If you cannot pass urine then you may need to have a . This is temporary.
Read about problems passing urine after prostate cancer treatment
Radiotherapy can irritate the lining of your . It can cause symptoms such as:
pain or bleeding from your rectum
leaking a slimy mucous discharge from your rectum
looser or more frequent or urgent bowel movements
Tell your doctor, nurse or radiographer if you have diarrhoea. They can prescribe medicine to help you.
Drink plenty of fluids. This helps to keep you hydrated.
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.
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. This includes problems getting an erection.
Last reviewed: 25 Jun 2025
Next review due: 25 Jun 2028
You have external radiotherapy for prostate cancer in a hospital radiotherapy department. You usually have it as an outpatient each weekday over 2 to 8 weeks.
You might have long term side effects after having external radiotherapy for prostate cancer. These include problems getting an erection and bowel and bladder problems.
You might have a type of internal radiotherapy called brachytherapy for prostate cancer. This means that you have a radioactive source inside the prostate.
Get practical and emotional support to help you cope with a diagnosis of prostate cancer, and life during and after treatment.
You may have a choice of treatments such as surgery or radiotherapy. Or your doctor might suggest that they monitor your cancer instead of treatment straight away.
Prostate cancer is cancer that starts in the prostate gland. The prostate gland is found at the base of the bladder and is about the size of a walnut.
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