External beam radiotherapy is a type of radiotherapy that is given from outside the body.

What is external beam radiotherapy?

  • External beam radiotherapy (EBRT) is a type of radiotherapy that is given from outside the body. It is usually given using a machine called a linear accelerator. The treatment is given by a radiographer.
  • Watch our short animation to learn more about external beam radiotherapy.

Important things to know

Who can have external beam radiotherapy?

You can have EBRT if: 

  • Your prostate cancer is contained within your prostate (localised or early stage).
T1 and T2 stage prostate cancer
  • Your cancer has spread to the area just outside the prostate (locally advanced).
T3 and T4 stage prostate cancer
  • You have had surgery and your PSA levels have started to rise or do not drop. You may hear this called salvage radiotherapy.
  • Your cancer has spread to other areas of your body, e.g. the bones. Radiotherapy can be used to control symptoms like bone pain.




How does external beam radiotherapy work?

  • EBRT uses high-energy X-rays to damage the prostate cancer cells. Cancer cells are not able to repair themselves very well. So, the radiotherapy can stop them from growing. 
  • Radiotherapy may kill some normal cells around the prostate, e.g. the bladder and bowel. This can cause side effects. But these normal cells are more able to recover. So, some side effects may get less over time.


What are the benefits of treatment?

  • You can have radiotherapy if you are not fit enough for surgery
  • It does not cause you any pain
  • The treatment sessions are quite quick
  • You can carry on working and doing your normal activities if you feel able 
  • You do not have to take time off work to recover
  • It can cure your prostate cancer if at an early stage
  • It can control prostate cancer that is not curable, alongside other treatments
  • It can help control symptoms caused by advanced prostate cancer, e.g. pain 
  • 99 out of 100 people who had radical radiotherapy were still alive at 10 years. 
Overall survival external beam radiotherapy
  • This figure is for those with Cambridge Prognostic Group 1, 2 and 3 localised prostate cancer. Ask your doctor or nurse specialist for your Cambridge Prognostic Group. Also take a look at our page on the grading and staging of prostate cancer (link will open in a new tab).
  • For more accurate and personalised information on the likely risk and benefit from treatment you can visit the Predict website (link will open an external tab). This site is best used with the support of a healthcare professional. 
Steve Radiotherapy
“The side effects are bad but you must compare them to not being alive. You are stronger than you think is something I was always told and you will get through this.”

Frequently asked questions (FAQs) about radiotherapy
  • There are different types of external radiotherapy. Your treatment team will recommend the type that is most suitable for you.  Ask your doctor or therapeutic radiographer about the type of radiotherapy you will be having. 


  • Types of external radiotherapy:
    • Conformal radiotherapy
    • Intensity modulated radiotherapy (IMRT)
    • Volumetric modulated arc therapy (VMAT)
    • Stereotactic radiotherapy. This is sometimes known as:
      • Stereotactic body radiotherapy (SBRT)
      • Stereotactic ablative radiotherapy (SABR)

Visit the Cancer Research UK website (this link will open in a new external tab) for more detailed information about each type.


Radiotherapy machines

  • Most radiotherapy is carried out using a Linac machine (linear accelerator). You may hear about machines called magnetic resonance linear accelerators (MR Linac). 
  • An MR Linac combines:
    • An MRI scanner and 
    • a linear accelerator
  • This lets the doctor look at the MRI images and deliver radiotherapy at the same time.
  • MR Linac are only available in a very small number of hospitals at the moment. 
  • You will have a CT scan two-to-three weeks before you start your treatment. This helps your doctor to plan your treatment.  
Black patient in CT scanner


  • A few freckle-sized tattoo marks will be made on your skin. These won’t wash off. This makes sure the radiotherapy is given to the same place each time. 
  • On the day of the CT scan and before each treatment you will need to:
    • Have a small enema to empty your bowel
    • Have a full bladder.
  • This moves your small bowel, rectum and bladder away from your prostate. This will reduce any side effects.
  • You may be at the hospital for an hour or two. This gives time for bowel and bladder preparation. The therapeutic radiographer needs time to line you up correctly in the machine. So, you will be in the treatment room for about 15–20 minutes. The treatment usually only takes about five minutes.
LInear accelerator radiotherapy machine
  •  For your first treatment:
    • You will usually have treatments daily from Monday to Friday
    • This will happen over a four–to-eight-week period
    • You will usually have between 20–40 treatments. 
  • If you are having radiotherapy for your bone pain, you may only need one treatment. 

The radiotherapy treatment is painless.

  • Having the planning tattoo may feel like a pin prick.
  • Your skin in the treated area may become slightly red, itchy, dry and sore. This can vary between people. Your healthcare team will give you advice on how to manage this. 
  • You will need to take time off work to go to your planning and treatment sessions. Otherwise, you can carry on working normally if you feel able to do so. 
  • You may be offered a course of hormone therapy injections with your radiotherapy. 

Facts about hormone therapy:

  • Hormone therapy can help to shrink your prostate and the cancer inside. This can help the radiotherapy to work better.
  • You may have the hormone therapy before, during or after your radiotherapy. Your doctor will decide on how long you need to take the hormone therapy. This can be from three months up to three years. 

Take a look at our page on hormone therapy to find out more. This link will open in a new tab.

  • Radiotherapy can damage your rectum. This is because it is very close to the prostate. This can cause side effects such as:
    • Runny poo (diarrhoea)  
    • Leaking poo (incontinence)
    • Blood in poo 
    • A red and swollen (inflamed) rectum.

Facts about rectal spacers:

  • Sometimes a ‘spacer’ is used to help to protect your rectum.
  • A spacer will help to move your rectum away from the treatment area. 
  • The most common type of spacer is a type of gel. The gel is injected into the space between your prostate and rectum. It is usually put in using a local anaesthetic. This means that the area around your back passage will feel numb.
  • The spacer will be put in before your radiotherapy starts. It will break down naturally (biodegrade). It will be absorbed by your body. This will happen over a few months. 
  • Currently, spacers are only used in certain hospitals. But soon they may be used in more hospitals. Ask your doctor about rectal spacers. 
  • In some hospitals, you will have special markers placed in your prostate before starting treatment. These are called fiducial markers. They can be made of gold or a special type of plastic. They are only about 3mm long.
  • Your prostate moves a little bit when:
    • You breathe
    • You need a poo
    • After you have had a poo.

Facts about fiducial markers:

  • The markers make sure that radiation points at the same area of your prostate at each treatment. 
  • They will stay in your prostate forever. 
  • They should not cause any problems. 
  • You can still have an MRI scan and go through airport security with no problem. 
  • They are put into your prostate one-to-two weeks before your planning CT. You will usually only have a local anaesthetic. Sometimes you may also get medicines that make you sleepy and help you to relax. This is called sedation. 
  • Radiotherapy can affect the amount and quality of your sperm. It may mean that you will have problems getting someone pregnant. 
  • If you think you may want children, please talk to your doctor before starting treatment. 
  • You may be able to have some of your sperm saved and frozen. This is called sperm banking or sperm cryopreservation. You can learn more about sperm banking on the Human Fertilisation and Embryology Authority website (this link will open in a new, external tab). 
  • Cancer Research UK also have information about sperm collection and storage (this link will open in a new, external tab). 


Image showing sperm freezing
  • You may still be able to get someone pregnant. 
  • There is a chance that the radiotherapy may damage your sperm. This may harm babies who are conceived during your treatment. So, you should use contraception during and after your course of radiotherapy. 
  • You can talk to your healthcare team for advice about safe sex during and after radiotherapy. 
  • You may also have problems getting and keeping an erection, and painful erections. You can get more information about sexual problems from your healthcare team. 

Our services search tool (this link will open in a new tab) will allow you to search for hospitals near you that offer external beam radiotherapy.

About this information

  • This information was published in March 2023. We will revise it in March 2024.
  • References and bibliography available on request.
  • If you want to reproduce this content, please see our Reproducing Our Content page.

What is risk?

  • Risk is the chance something bad could happen when we do something. Even simple things such as walking down the stairs can have risks. But we take risks because we think it will be worth it. We need to think about both the benefits and risks of what might happen when we do something.
  • You should always ask your healthcare team about both the benefits and risks of any treatment.
  • Remember if they tell you about a risk, it doesn’t mean it will happen to you. They may say one man in ten who has this treatment will have a side effect. But they can’t tell you if you will be the ‘one’ man who gets this side effect.
Risk vs Benefit
problems peeing
Problems pooing

This data is for people with CPG 1, 2 and 3 localised prostate cancer. Click here to learn more about CPG groups (this will open in a new tab).

Sexual risks

This data is for people with CPG 1, 2 and 3 localised prostate cancer. Click here to learn more about CPG groups (this will open in a new tab).

  • The information on the risks comes from very large clinical studies. These typically involved thousands of people being watched over many years. 
  • There may be local data from your area. You can ask your healthcare team if they have this information too. 

About this information

  • This information was published in March 2023. We will revise it in March 2024.
  • References and bibliography available on request.
  • If you want to reproduce this content, please see our Reproducing Our Content page (this page will open in a new tab).

What is the impact?

  • We asked real visitors to the infopool to share their experience of this treatment. They told us how this treatment had impacted their everyday lives in a number of different areas.
  • The numbers and images below represent how many people said this treatment had impacted them ‘a lot’ in each of the different areas.
  • For example, imagine it says ‘25 in 100’ underneath ‘physical and social ’. This means that 25 out of 100 people who shared their experience of this treatment told us it impacted their ‘physical and social ’ a lot. However, it would also mean that 75 out of 100 people said it had not impacted them a lot.

Physical and social wellbeing

Enjoying activities such as walking or going out to the pub

77 out of 100

Effect on relationships

Ability to make good connections with others

55 out of 100

Sexual activity

Ability to reach sexual arousal, either physically or emotionally

73 out of 100

Sense of self

Knowing who you are and what motivates you

61 out of 100

Wellbeing and quality of life

Feeling good and functioning well in your personal and professional life

66 out of 100

Mental and emotional health

Ability to think clearly, make good decisions, and cope with your emotions

66 out of 100


Feeling of constant physical and/or mental tiredness or weakness

81 out of 100