What are the side effects of external beam radiotherapy?
Like all treatments for prostate cancer, radiotherapy can cause side effects. These will affect each man differently, and you might not get all the possible side effects.
Side effects happen when the healthy tissue near the prostate is damaged by radiotherapy. Most healthy cells recover so side effects may only last a few weeks or months.
Some side effects can start months or years after treatment. These can sometimes become long-term problems. Sometimes long-term or late side effects after radiotherapy treatment are called pelvic radiation disease. Read more about pelvic radiation disease on the PRDA website.
Before you start treatment, talk to your doctor, nurse or therapeutic radiographer about the side effects. Knowing what to expect can help you deal with them.
If you have hormone therapy as well as radiotherapy, you may also get side effects from the hormone therapy. Read more about the side effects of hormone therapy and how you can manage them.
The most common side effects of radiotherapy are described below.
Short-term side effects
Urinary problems
Radiotherapy can irritate the lining of the bladder and the urethra, which is the tube men urinate (wee) and ejaculate through. It can also cause swelling in the prostate. This can cause urinary problems, such as:
needing to urinate often, including at night
a sudden urge to empty your bladder
reduced flow
a burning feeling when you urinate
difficulty urinating (urine retention)
blood in your urine.
You might also leak urine (urinary incontinence) after radiotherapy, but this is rare. It may be more likely if you’ve previously had an operation called a transurethral resection of the prostate (TURP) for an enlarged prostate.
Urinary problems tend to start midway through your treatment and may begin to improve several weeks after treatment finishes. But this is different for everyone.
Some men may continue to have side effects for longer, while others may not get any side effects at all or have side effects that improve more quickly.
If you get any urinary problems, tell your doctor, nurse or therapeutic radiographer. There are treatments to manage them, as well as things you can do to help yourself.
Your medical team may suggest pelvic floor muscle exercises that could help with your urinary problems. You can usually do these at home.
Bowel problems
Radiotherapy can irritate the bowel and back passage because these areas sit close to the prostate. This irritation is called proctitis, which can cause bowel problems.
Before starting radiotherapy, tell your doctor if you’ve had any bowel problems in the past, as this may increase your risk of getting bowel problems again.
Symptoms vary from person to person, and some men only notice slight changes.
Common bowel problems can include:
passing more wind than usual, which may sometimes be wet
loose or watery bowel movements (diarrhoea)
needing to empty your bowels more often, or having to rush to the toilet
leaking a clear, jelly-like mucus from your back passage
feeling an urge to empty your bowels, but then not being able to
a feeling that your bowels haven’t emptied properly
pain in your abdomen (stomach area) or back passage
bleeding from your back passage – this isn’t usually anything to worry about, but let your doctor, nurse or therapeutic radiographer know if it happens
leaking from your back passage (faecal incontinence) – this is very rare.
Bowel problems usually start during or shortly after your treatment and usually begin to settle down several weeks after finishing treatment. Again, this is different for everyone.
Some men may continue to have side effects for longer, while others may not get any side effects at all or may find their side effects improve more quickly.
Tell your doctor, nurse or therapeutic radiographer about any changes in your bowel habits. There are simple treatments to manage them, as well as things you can do to help yourself.
If you have anal sex, bowel problems after radiotherapy may affect your sex life. You can continue giving anal sex to your partner. But if you receive anal sex, your doctor, nurse or therapeutic radiographer may suggest you avoid having anal sex while you're having radiotherapy, and for at least two months afterwards. This is to make sure any bowel problems or sensitivity have settled before receiving anal sex and will be different for everyone. Find out more about how side effects of prostate cancer treatment may affect your sex life if you have anal sex or you’re a gay or bisexual man.
Screening for bowel cancer
Radiotherapy can sometimes cause temporary changes in your bowel, such as bleeding, which could affect the result of your NHS bowel screening test. Some people may be advised to wait a short time after treatment before doing the test, but this depends on individual circumstances. If your screening invitation arrives soon after radiotherapy, speak to your GP or hospital team for advice. It’s important that you don’t miss your screening.
It’s normal to have a tiny amount of blood in your bowel movements while having radiotherapy and this shouldn’t be anything to worry about. But if you’re having radiotherapy and you do notice blood you should always let your therapeutic radiographer, or the doctor know.
Not all men get urinary or bowel problems after radiotherapy. But if you do, it shouldn’t stop you from travelling. The following tips may help you plan ahead and feel more prepared for your trip.
Try to book an aisle seat close to toilets and find out where the nearest public toilets are.
If you use pads, make sure you pack enough for your trip.
Keep a spare change of clothes and an empty plastic bag with you to store wet clothes.
Wear dark trousers if you’re worried about leaks.
Carry some hand gel and a pack of wet wipes or tissues when travelling – supermarkets sell these in small sizes that are easy to carry.
Use our urgent toilet card to help you get to a toilet quickly.
You can buy a radar toilet key for locked public toilets.
Tiredness and fatigue
Radiotherapy can make you feel very tired, especially towards the end of your treatment. Fatigue is extreme tiredness that can affect your everyday life. It can affect your energy levels, your motivation and your emotions – which can be hard to cope with.
Read more about ways to manage your fatigue.
Problems with ejaculation
You may find ejaculation uncomfortable and notice that you produce less semen during and after treatment. You may also have a ‘dry orgasm’, where you feel the sensation of orgasm but don’t ejaculate. This may feel different to the orgasms you’re used to and some men find this difficult to come to terms with.
Skin irritation and hair loss
During treatment, the skin between your legs and near your back passage may become sore or look a bit like sunburn – but this is rare. Your radiographer will talk to you about how to look after your skin during treatment. Radiotherapy might also make some of your pubic hair fall out. But it usually grows back after treatment.
Long-term or late side effects
Sometimes side effects can develop months, or even years after treatment has finished. If this happens, then these side effects can last a long time.
Talk to your doctor or nurse about your own risk of long-term side effects. You might be more likely to get them if:
you’re older
you have diabetes
you’re very overweight
you’ve had bowel or prostate surgery in the past
you’ve had bladder, bowel or erection problems in the past.
Some studies suggest smoking may increase the risk of long-term bowel and urinary problems after radiotherapy, but more research is needed.
Urinary problems
If you had urinary problems during treatment, you may be more likely to develop problems later on. These may be similar to the short-term side effects listed above.
Radiotherapy can cause the urethra to become narrow over time – this is called a stricture. This is more likely if you have brachytherapy combined with external beam radiotherapy. If this happens, you may find it difficult to urinate.
Symptoms can include:
feeling that your abdomen (stomach area) is swollen
feeling that you’re not emptying your bladder fully
a weak flow when you urinate.
Speak to your doctor or nurse if you get any of these symptoms. Find out more about urinary symptoms.
Bowel problems
Although bowel problems often improve once treatment has finished, some men find that changes to their bowel habits last a lot longer.
Bowel problems can develop months or years after treatment and may be similar to the short-term side effects listed above. If you had bowel problems during treatment, you may be more likely to develop problems later on.
Try not to be embarrassed to tell your hospital doctor or your GP about any bowel problems. There are treatments that can help. Bowel problems can be common in older men, so it’s possible that they’re caused by something other than radiotherapy. Your hospital doctor or your GP can arrange tests to find out what’s causing the problems, or they may refer you to a bowel specialist.
If you have long-term bowel problems, you might be offered a camera test, such as a flexible sigmoidoscopy or a colonoscopy. This is where a narrow tube with a camera on the end is put into your back passage to check for any damage to the bowel.
Erection problems
Radiotherapy can cause problems getting or keeping an erection (erectile dysfunction). Other treatments for prostate cancer such as hormone therapy, other health problems, certain medicines, tiredness and fatigue, and depression or anxiety can all cause erection problems too. And many men with prostate cancer may have had sexual problems before their treatment.
Erectile dysfunction caused by radiotherapy often takes a while to appear and it can be up to two years before you notice any problems. Erection problems can also get worse over time.
There are lifestyle changes and treatments that may help manage erection problems or sometimes prevent them. For example, your doctor may prescribe regular medication to help with erectile dysfunction after your radiotherapy. These often work best if you start them soon after radiotherapy. Talk to your doctor, nurse or therapeutic radiographer to find out more.
Find out more about erection problems, including what treatment is available and practical tips to help with your sex life.
Having children
Radiotherapy can damage the cells that make semen and cause you to have a dry orgasm (where you don’t ejaculate). You may want to consider storing your sperm before you start radiotherapy, so that you can use it later for fertility treatment – if you want to. Ask your doctor, nurse or therapeutic radiographer about sperm storage.
There is a very small chance that radiotherapy could affect any children you might conceive during treatment. If there is a chance of your partner getting pregnant, you may want to use contraception over the period you are having radiotherapy and for up to a year after. You can also ask your doctor, nurse or therapeutic radiographer for advice. It is safe for you to have sex with your partner – you won’t pass on your cancer or any radiation.
Lymphoedema
If your lymph nodes are treated with radiotherapy, there is a small chance that fluid might build up in your tissues. This is called lymphoedema. It usually affects the legs, but it can affect other areas, including the penis or testicles. It can occur months or even years after treatment. Speak to your doctor or nurse if you start to get any unusual swelling.
Hip and bone problems
Radiotherapy can damage the bone cells and the blood supply to the bones near the prostate and the pelvic lymph nodes. This can cause pain, and hip and bone problems later in life. Hormone therapy can also weaken your bones, so you might be slightly more likely to have hip and bone problems if you have both hormone therapy and radiotherapy.
Other cancers
Radiotherapy can damage the cells in the tissues surrounding the prostate. There is a very small chance that this could increase your risk of bladder or bowel cancer. It would take at least 5 to 10 years after having radiotherapy treatment for a second cancer to appear.
References and reviewers
Updated: March 2026 | Due for Review: March 2029
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Marguerite Bingle, Prostate Cancer Clinical Nurse Specialist, East Suffolk & North Essex NHS Foundation Trust
Deirdre Dobson, Deputy Head of Radiotherapy, Guy’s Cancer at Queen Mary’s Hospital
Oliver Hulson, Consultant Radiologist, St James University Hospital, Leeds
Joe O’Sullivan, Consultant Oncologist, The Northern Ireland Cancer Centre, Belfast
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