External radiotherapy for prostate cancer

man going into a radiotherapy machine

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External radiotherapy uses high-energy rays to kill cancer cells. The radiation beams are aimed at the cancer using a machine called a linear accelerator. 

The aim of radiotherapy for early prostate cancer is to fully get rid of your cancer.

Who can have radiotherapy?

The treatment is suitable if your prostate cancer is found only within your prostate gland or has spread just outside it to the pelvic lymph nodes.

Radiotherapy and hormone therapy are often used together to treat locally advanced prostate cancer. This helps to make the radiotherapy work better at controlling your prostate cancer.

It may not be the best option if you have urinary symptoms, as it may make them worse.

Before radiotherapy

You will go to the hospital before treatment for planning. An important part of the planning process is simulation. This involves using a CT scanner to pinpoint the area to be treated.

The treatment field or area will be marked carefully on your skin, usually using tiny tattoo dots. You might also have gold markers called fiducials put into your prostate to make sure the radiotherapy targets the right area. These are put into your prostate gland under anaesthetic before the treatment starts.

To make sure your prostate is in the same position each time, you may have to follow a special diet, drink some water just before your treatment, or have an enema. An enema is a fluid solution gently inserted into your bowel through your back passage, which causes you to clear your bowels.

Having radiotherapy 

During treatment you will first be positioned carefully on a treatment table. Then the machine will move around you so that you receive the precise treatment at different angles or in an arc. The treatment normally takes several minutes and is painless. 

Most people receive radiotherapy as outpatients, travelling to the radiotherapy unit each day, with a break at weekends. 

The course can be several treatments over a number of days or weeks (usually 4 to 8 weeks). 

External radiotherapy does not make you radioactive. It is completely safe for you to mix with family and friends, including pregnant women and children.

Stereotactic radiotherapy

Stereotactic radiotherapy is a type of radiotherapy that targets the cancer very precisely with high doses of radiation.  Because each stereotactic treatment gives a high dose of radiation, a treatment course is usually much shorter. 

Your radiation oncologist will give you more detailed information if he or she recommends this type of radiotherapy for you.

Radiotherapy side-effects 

If you get any side-effects, they usually develop during or shortly after your treatment and get better within a few weeks. These are called short-term or acute side-effects. It’s also possible to get late side-effects, which develop some time after treatment. Some side-effects last for a long time or may even be permanent, but it is rare to have long-term problems.

Short-term or acute side-effects

  • Urinary problems 
  • Bowel problems
  • Fatigue (tiredness)

Urinary problems

  • A burning sensation when you pass urine.
  • Needing to pass urine more often.
  • Blood in your urine.

Read more about urinary symptoms and how to manage them 

Bowel problems

  • Diarrhoea (loose, semi-solid bowel movements). 
  • Constipation (not having a bowel movement often enough).
  • Cramping pain in your tummy.
  • Passing more wind or mucus.
  • Needing to get to the toilet more quickly.
  • Mild bleeding when you go to the toilet.

Read more about coping with side-effects and symptoms

Fatigue (tiredness)

You may experience tiredness from the anaesthetic or from getting up a lot at night to pass urine. It usually takes a few months for this to improve after treatment. Read more about coping with fatigue.

Late, long-term or permanent side-effects

  • Erectile dysfunction (impotence).
  • Urinary problems. 
  • Bowel problems.
  • Infertility /  ‘Dry’ orgasm.

Erectile dysfunction 

  • Finding it hard to get or keep an erection.

Erectile dysfunction can happen because radiotherapy can damage the nerves and blood vessels that control erections.

You’re more at risk of erectile dysfunction if you have had erection problems before your treatment or if you have hormone therapy as well as radiotherapy.

Can early treatment help erection problems?

There is some evidence that taking tablets or using vacuum therapy for erectile dysfunction soon after radiotherapy may reduce your risk of erectile problems.  You may not be interested in sex at first. But taking the tablets or using a vacuum pump at an early stage may improve your chances of getting erections if and when you are ready to have sex again.

Read more about erectile dysfunction and how to manage it.

Urinary problems

  • Needing to go to the toilet more often.
  • Pain when passing urine. 
  • Blood in your urine.
  • Narrowed water pipe (urethra), which can make it hard to pass urine.
  • Leaking urine. This is rare unless you had surgery too. 

It’s rare for the bladder to be permanently affected by radiotherapy. Narrowing of the urethra needs to be treated with surgery. If you notice any bleeding or other symptoms, tell your doctor so that tests can be done to check the cause and decide if any treatment is needed.

Bowel problems

  • Diarrhoea (loose, semi-solid bowel movements). 
  • Feeling an urge to empty bowels but not being able to or feelings that the bowels haven’t emptied properly.
  • Passing clear or jelly like mucus.
  • Needing to get to the toilet more quickly.
  • Needing to get to the toilet more often.
  • Bleeding when you go to the toilet.

Bowel problems may carry on or appear years after treatment.  Your bowel habits may change permanently. 

Bowel problems are common in older men, so symptoms may be due to something else. But it’s important to tell your doctor about symptoms such as diarrhoea or bleeding. You may need to have tests to find out the cause or have treatment to help. 

Infertility / ‘Dry’ orgasm

  • Less or no semen when you ejaculate

Dry orgasm means you won’t be able to father a child, as there is no semen. Read more about infertility. Talk to your doctor before your treatment if you’re worried about this. It’s not safe to assume you are sterile, so you will need to use contraception to avoid pregnancy.

Read more about fertility and cancer treatment.

Advantages and disadvantages of external beam radiotherapy


  • You don’t need a general anaesthetic and you don’t need to stay overnight in hospital. 
  • You may be able to work and carry on normal activities during the treatment.
  • You are not radioactive during or after the treatment so you can be in close contact with others.
  • Each treatment is relatively short. It usually takes about 15 minutes, although you may be in the radiotherapy department for up to an hour.


  • It may be difficult if you have far to travel to the radiotherapy unit.
  • It may take some time to see how effective the radiotherapy has been.
  • You may not be able to have prostate surgery in the future due to the effects of the radiotherapy.
  • You might experience side-effects such as bowel or urinary problems, erectile dysfunction and fatigue. Some of these side-effects may develop or get worse over the longer term.
  • You may become infertile.
  • Treatment may very slightly increase the risk of getting a second cancer.

For more information

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