Externa beam radiotherapy for prostate cancer
Most radiotherapy side effects gradually go away in the weeks or months after treatment. But long term side effects can continue. Or you might notice that some side effects begin months or years later.
Everyone is different and the side effects vary from person to person. You may not have all of the effects mentioned. Tell your doctor or nurse if you have any of these problems. They can help you to find ways of controlling the effects.
Before treatment, your doctor will explain the risk of you getting side effects. But they won’t be able to tell you whether any of these side effects will definitely happen to you. Some side effects are more likely in some people.
Your risk of side effects is higher if you have brachytherapy as well as external radiotherapy.
Find out more about external radiotherapy for prostate cancer
You might have problems passing urine after the radiotherapy ends. It might gradually get harder to pass urine over a few weeks or months. This is due to the treatment causing a narrowing of the tube from the bladder to the penis (the urethra). The narrowing is called a urethral stricture.
You might be able to have a short operation to widen the urethra if this happens. Speak to your doctor if you find it hard to pass urine.
A small number of men find they can’t pass urine at all. Tell your doctor straight away if this happens.
After radical radiotherapy, you might have some problem with leaking urine. For most of these men, the problem is occasional dribbling of urine. Your doctor or nurse can refer you to a specialist incontinence clinic if this becomes a problem. They can help you with muscle exercises, bladder training and medicines.
Some men find that they can’t control their urine at all. This is very uncommon. If it happens you need to have a tube called a catheter into your bladder. The tube drains the urine into a bag.
Read more about managing bladder problems after prostate cancer treatment
Radiotherapy can damage the nerves that control getting an erection.
Whether you have problems getting and keeping an erection depends on several factors. These include:
your age (impotence is less likely if you are under 65)
whether you have other health conditions
whether you had erection problems before the treatment
if you have hormone therapy before or after the radiotherapy
whether you have internal radiotherapy as well as external radiotherapy
Tell your doctor or specialist nurse as soon as possible if you have erection problems. Early treatment with medicines such as sildenafil (Viagra) might help you to get and keep erections. If you continue to have problems, they can refer you to a specialist to help with this.
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.
Inflammation of the back passage (rectum) is called proctitis. This is a possible long term side effect. Proctitis can cause:
a feeling of wanting to strain whether or not you actually need to pass a bowel movement
bleeding from your rectum
a slimy mucous discharge from your rectum
Talk to your doctor or specialist nurse if you have any of these side effects. They will be able to refer you to a specialist team to check the cause. They can help you to find ways of controlling the effects.
Read more about treating diarrhoea during and after radiotherapy treatment
You might get swelling in the legs or the sack of skin around the testicles (the scrotum). The swelling is called lymphoedema (pronounced lim-fo-dee-ma).
The risk of lymphoedema is greater if you have radiotherapy to your as well as your prostate. The radiotherapy can damage the lymph channels that drain fluid from your legs. The swelling can be uncomfortable.
You can do various things to lower your risk of getting lymphoedema. Early treatment can reduce the swelling and stop it from getting worse.
A small number of men develop bladder cancer or cancer of the lower bowel (rectum) after radiotherapy for prostate cancer. This can happen many years after treatment.
It is important that you contact your GP if you notice blood in the urine or poo or a change in your bowel habits.
Rarely, radiotherapy can damage the bone cells in the pelvic area. It can 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 can sometimes make it hard to walk or climb stairs.
Your doctor will monitor you. They may check your bone strength with a . They might suggest treatment with painkillers and walking aids to help you get around. You might also need to take medicines to strengthen the bones. These are called . These drugs can help to control pain and reduce the risk of fractures.
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.
Speak to your doctor if you have any pain in your bones. The pain usually gets worse if you move around or do exercise and gets better when you sit still or rest. Your doctor might ask you to have x-rays, a CT scan or an MRI scan to see if there are any fractures in the bones.
Coping with the side effects of prostate cancer radiotherapy can be difficult. There are things you can do, and people who can help you and your family to cope.
Find out more about coping and support when you have prostate cancer
Last reviewed: 27 Jun 2025
Next review due: 27 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.
Radiotherapy to the prostate can cause some side effects. These include loose or watery poo (diarrhoea) and problems passing urine.
You might have a type of internal radiotherapy called brachytherapy for prostate cancer. This means that you have a radioactive source inside the prostate.
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.
Get practical and emotional support to help you cope with a diagnosis of prostate cancer, and life during and after treatment.
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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