Side effects of external beam radiotherapy

Radiotherapy to the prostate causes different side effects. Most of these usually improve gradually after treatment has finished. Always tell your cancer team about your side effects.  There is often something they can do to improve them. They can give you advice on how to manage them.

Side effects include:

  • Tiredness – this may last for up to a couple of months after treatment is over.
  • Skin changes – the skin in the treated area may become red or darken, or become flaky and itchy.
  • Bladder effects - you may feel you need to pass urine more often or have pain passing urine.
  • Bowel effects – you may get diarrhoea and sometimes pain in the back passage.

Some side effects may not improve or certain side effects develop months or years after radiotherapy. These are called late effects. Some men may gradually develop problems getting and keeping an erection years after treatment. Your doctor will explain more about this and tell you about treatments that can help. Other late effects can include bladder or bowel problems.

Side effects of external-beam radiotherapy

Side effects usually build up slowly after you start treatment. They may continue to get worse for a couple of weeks after treatment. But after this, most side effects improve gradually over the next few weeks.

Your doctor, nurse, or radiographer will talk to you about this. They will explain what to expect and give you advice on what you can do to manage side effects. Always tell them about your side effects. There are usually things they can do to help. We list the common side effects here, but you may not get all of these.

We have more detailed information about pelvic radiotherapy.


Radiotherapy causes tiredness, especially towards the end of treatment. It may last for a couple of months or longer after treatment has finished. Make sure you get plenty of rest. But try to balance this with regular physical activity, such as short walks. This will help give you more energy.

Effects on the skin

The skin in the treated area may become red (if you have light skin) or darker (if you have dark skin). It may also become dry, flaky, and itchy. Sometimes the skin around the back passage (rectum) and scrotum becomes moist and sore. The radiographer or your specialist nurse will tell you how to look after the skin in the treated area. They can prescribe a cream or dressings and painkillers if you need them. Always tell them if your skin is sore or you have other changes.

Your pubic hair may fall out. It usually starts to grow back a few weeks after you have finished treatment. It may be thinner than before.

Effects on the bladder

Radiotherapy can also cause inflammation of the bladder (cystitis). You may:

  • feel you want to pass urine (pee) more often
  • have a burning feeling
  • have urgency when you pass urine.

Your doctor can prescribe medicines to help. Drinking 2 to 3 litres (3½ to 5½ pints) of fluids a day can help. Avoid drinks containing caffeine and alcohol.

These side effects usually disappear slowly a few weeks after treatment has finished.

Occasionally, men may have difficulty passing urine and need to have a tube put into the bladder to drain urine (urinary catheter). Rarely, some men may have some leakage of urine (incontinence). Let your nurse or radiographer know if this happens.

Some men who had urinary problems when they were diagnosed may find these improve a while after their radiotherapy finishes.

Effects on the bowel

Radiotherapy to the prostate can irritate the back passage (rectum) and bowel. You may get diarrhoea, wind and cramping pains in your tummy (abdomen). Your doctor can prescribe medicines to help control these side effects. Some men get pain in the back passage and may have some bleeding.

If you have diarrhoea, drink at least 2 to 3 litres (3½ to 5½ pints) of fluids a day. Avoid caffeine and alcohol. Your nurse or radiographer may advise you to make some changes to your diet during treatment, such as eating less fibre.

Possible late effects of external-beam radiotherapy

Some men may have side effects that do not improve, or side effects that happen months to years after radiotherapy finishes. These are called long-term or late effects. Your doctor or nurse will explain these to you. There are different ways late effects of pelvic radiotherapy can be managed.

Erection problems

Radiotherapy for prostate cancer can cause problems getting or keeping an erection. This is called erectile dysfunction (ED). Your age and whether you are taking hormonal therapy can also affect how likely you are to get ED.

ED may not happen straight after treatment. It can develop slowly over 2 to 5 years. Ask your cancer doctor about your risk of ED. If you develop ED, there are different treatments that can help.

After radiotherapy and brachytherapy, some men ejaculate little or no semen.


Radiotherapy to the prostate may cause permanent infertility. Some men may find this difficult to cope with. If you are worried, talk to your cancer doctor. You may be able to store sperm before treatment starts.

Bowel and bladder problems

Some men may have bowel or bladder changes because of radiotherapy. For example, blood vessels in your bowel and bladder can become more fragile. This may cause blood in your urine or from the back passage (bottom). If you notice any bleeding, always tell your doctor so they can check it out.

Let them know about any bowel or bladder symptoms you have. They can give you advice and may do some tests. You may also find it helpful to contact the Bladder and Bowel Community for support.

Bowel changes can include diarrhoea, wind, or constipation. Rarely, some men have difficulty controlling their bowels and may have some leakage (faecal incontinence). These symptoms can often be managed with medication and changes to your diet. If the problems do not improve, you can ask to be referred to a bowel specialist (a gastroenterologist or bowel surgeon).

The symptoms of bladder irritation that happen during treatment may not stop completely. Rarely, some men may get leakage of small amounts of urine (urinary incontinence). Your doctor can arrange for you to see a specialist continence nurse or physiotherapist for advice.

Macmillan toilet card

If you need to use a toilet urgently, you can show this card in places such as shops, offices, cafés, and pubs. You can use it during or after treatment. We hope it allows you to get access to a toilet without any awkward questions. But we cannot guarantee that it will work everywhere.

Back to External beam radiotherapy for early prostate cancer

What is external beam radiotherapy?

External beam radiotherapy is the most common type of radiotherapy. A big machine directs external radiotherapy beams at the affected area.