What is radiotherapy?

Radiotherapy uses high-energy rays to treat cancer. It destroys cancer cells in the area where the radiotherapy is given. The aim of radiotherapy for prostate cancer is to try to cure the cancer or control it for many years. Doctors call this radical radiotherapy. At the same time, they try to make sure radiotherapy causes as little harm as possible to healthy tissue and organs close by. These include the bladder, back passage (rectum) and bowel.

Radiotherapy for prostate cancer can be given in different ways:

External beam radiotherapy is the most common way of giving radiotherapy for prostate cancer. Sometimes it is given with brachytherapy.

You may be given hormonal therapy before, during and after radiotherapy. It helps make radiotherapy more effective.

We have separate information on radiotherapy for advanced prostate cancer.


If you smoke, it is important to try to stop. Stopping smoking can make radiotherapy work better. It also reduces the side effects of treatment. It can be difficult to stop smoking, but you can get support. We have more information to help you give up smoking.

Having radiotherapy for prostate cancer

You have external beam radiotherapy as an outpatient in the radiotherapy department. Radiotherapy is given using a machine that is like a big x-ray machine. This is called a linear accelerator (often called a LINAC).

You usually have it as a series of short, daily treatments. The treatments are given from Monday to Friday, with a rest at the weekend. Radiotherapy is not painful, but you will need to lie still while you have it.

You may have radiotherapy over either:

  • 4 weeks – the dose you get for each treatment session is higher.
  • 7 weeks – the total overall dose of radiation is higher.

Both ways are effective, and the side effects are the same. You usually have radiotherapy over 4 weeks as it is a shorter treatment.

If you have a type of radiotherapy called stereotactic ablative radiotherapy (SABR) you have it over a much shorter time.

Your doctor or nurse will explain how long your course of radiotherapy will take. It is safe for you to be with other people during external radiotherapy, including children.

Types of radiotherapy for prostate cancer

There are different techniques used to treat prostate cancer more effectively. They treat the cancer while protecting healthy tissue and reducing side effects.

  • Intensity-modulated radiotherapy (IMRT)

    IMRT is usually the type of radiotherapy you have. It uses advanced computers to calculate and deliver radiation directly to the cancer from different angles. IMRT shapes the radiation beams to the size of the tumour. The strength (intensity) of the dose can be changed depending on the tissue. Doctors can deliver an even higher radiation dose to the cancer while giving lower doses to healthy tissue.

  • Volumetric modulated arc therapy (VMAT)

    VMAT is a newer technique that works in a similar way to IMRT. The radiation dose can be changed even more accurately during treatment. The machine rotates around you and quickly delivers radiotherapy beams in continuous arcs (curves) precisely to the cancer. VMAT can be given in shorter treatment sessions. It is currently only available in some hospitals. Doctors still need to find out if it is as effective as IMRT.

  • Stereotactic ablative radiotherapy (SABR)

    SABR allows large doses of radiotherapy to be given very precisely to small areas. SABR uses many smaller, thin beams of radiation. The beams are directed from different angles that meet at the tumour. It can deliver large doses of radiation to the prostate. This means you have all your treatment over a few days, instead of weeks.

    SABR is not a standard treatment for prostate cancer, but it is currently being used in several hospitals. It does not seem to cause an increase in side effects.

Planning radiotherapy for prostate cancer

Your cancer doctor plans your radiotherapy carefully to make sure it is as effective as possible. During the planning visit, you will have a CT scan.

Having your planning scan

The scan will help your doctor work out the exact dose and area of your treatment.

Before your scan, you may need to have a special diet or take medicine to empty your bowel. You may also need to drink water to fill your bladder. This is to get very clear CT pictures to help plan your treatment.

You may also have a very small amount of liquid passed into your rectum (enema) to empty your bowel. You may need to do this before each session of radiotherapy.

During the scan, you need to lie still in the same position you will be in for your radiotherapy.

Tattoo marks

The person who gives you your treatment (radiographer) will make some permanent marks (tattoos) the size of a pinpoint on your skin. These make sure you are in the correct position for every treatment session and show where the beams will be directed.

We have more information about planning radiotherapy.

Other treatment planning

Your doctor may talk to you about having some of the following or you may hear about these:

  • Fiducial markers

    Sometimes you may have tiny gold grains (called fiducial markers) passed into your prostate using an ultrasound probe. They help the radiographer see the position of the prostate before each session. This may help reduce side effects and any possible damage to organs close to the prostate. They are often used with SABR.

  • Rectal spacers

    A small amount of liquid gel, or an inflatable biodegradable balloon, is put into the space between the prostate and rectum. This moves the rectum away from the prostate and reduces the amount of radiation reaching the rectum. This helps reduce bowel side effects. It stays in place during radiotherapy and is gradually absorbed by the body.

    You need a general anaesthetic to have this done. The doctor injects the spacer as a liquid through a small needle between the rectum and the prostate. After it you may be a bit sore at the injection site for a short time. You may need to take antibiotics to reduce the risk of infection.

    There is a very small risk of complications if the spacer is not injected correctly. This may delay your treatment. Your doctor will explain the possible risks and benefits. Rectal spacers are approved by the National Institute for Health and Care Excellence (NICE) but are not available in all hospitals. You can talk to your doctor about this. They may be available through private healthcare.

  • Image-guided radiotherapy (IGRT)

    This is done when you have radiotherapy. To make sure the treatment is delivered precisely, the radiographers take images before or during each session of radiotherapy. These show the size and shape of the cancer and make sure the cancer is in the same position as in your planning scan.

Having radiotherapy

The radiographer will explain what will happen. At the start of each treatment session (called a fraction), they make sure you are in the correct position on the couch and that you are comfortable.

When everything is ready, they leave the room so you can have the radiotherapy. The treatment only takes a few minutes. You can talk to the radiographers through an intercom or signal to them during the treatment. They can see and hear you from the next room.

During treatment, the radiotherapy machine may automatically stop and move into a new position. This is so the radiotherapy can be given from different directions.

Side effects of radiotherapy for prostate cancer

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

Your radiotherapy team will explain what to expect and give you advice on how to manage side effects. Always tell them about your side effects. There are usually things they can do to help.

Side effects that do not go away or develop years later are called late effects (see below).

Immediate side effects

We list the common side effects here. You may not get all of these.

  • Bowel effects

    Radiotherapy to the prostate can irritate the back passage (rectum) and bowel. You may get:

    • diarrhoea
    • wind
    • cramping pains in your tummy (abdomen)
    • pain and sometimes bleeding from the rectum.

    Your doctor can prescribe medicines to help control these side effects.

    If you have diarrhoea, drink at least 2 to 3 litres (3½ to 5½ pints) of fluids a day. Avoid caffeine and alcohol. You may be advised to make some changes to your diet such as eating less fibre.

  • Bladder effects

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

    • feel you want to pass urine (pee) more often (frequency)
    • have a burning feeling or you may be unable to wait to empty your bladder (urgency).

    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.

    If you have difficulty passing urine you may need a tube put into the bladder to drain urine (urinary catheter) until side effects improve. Urinary problems you had when you were diagnosed may improve after radiotherapy.

  • Tiredness

    You may get tired, especially towards the end of treatment. It may last for a couple of months or longer. Get plenty of rest. Try to balance this with regular physical activity, such as short walks.

  • 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 nurse will give you advice. They can prescribe a cream or dressings and painkillers if you need them. 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.

Related pages

Possible late effects of prostate radiotherapy

Side effects that do not improve or happen months to years after pelvic radiotherapy are called long-term or late effects. Improved ways of giving radiotherapy, such as Intensity-modulated radiotherapy (IMRT), help to reduce the risk of late effects, particularly on the bowel.

Your doctor or nurse will explain these to you. You can read more about how late effects of pelvic radiotherapy can be managed.

  • Erection problems

    Radiotherapy to the pelvis can cause problems getting or keeping an erection. This is called erectile dysfunction (ED). It may not happen straightaway but can develop slowly over 2 to 5 years. Different things increase the risk of ED, for example if you are older, or are also taking hormonal therapy drugs which affect your desire to have sex. We have more information about other factors that can increase the risk of ED.

  • Bowel late effects

    These may be like the immediate side effects. You may need to rush urgently to go to the toilet. Rarely there may be some leakage or soiling (bowel incontinence). Sometimes blood vessels in the bowel lining become fragile and bleed. If you have any bleeding always tell your doctor so they can check it. We have more information about managing managing bowel late effects.

  • Bladder late effects

    The bladder irritation may not completely go away or may develop later. The bladder lining may bleed easily, causing blood in your urine. Rarely you may get leakage of small amounts of urine (urinary incontinence). We have more information about managing bladder problems.

  • Infertility

    Radiotherapy to the prostate may cause permanent infertility. You may be able to store sperm before treatment starts.

PSA levels after external radiotherapy

After radiotherapy, it can take time for your PSA level to drop. It usually goes down gradually. It may not get to its lowest level until about 18 months or longer after treatment. Your doctor and nurse can give you more information.

Benefits and disadvantages of external beam radiotherapy for early prostate cancer

Radiotherapy and a radical prostatectomy may both cure early prostate cancer. Your doctor may ask you to choose between two treatments.

It can help to understand what each treatment involves and to look at the benefits and disadvantages of each one. You may also want to think about the immediate and possible long term effects. After this, you can decide along with your doctor.

Benefits of external beam radiotherapy

You do not need surgery or a general anaesthetic, which may have risks if you have other health conditions. You can keep doing most of the daily things you usually do. Urinary problems may happen less often than after a prostatectomy.

Disadvantages of external beam radiotherapy

You need to go to hospital as an outpatient for 4 to 7 weeks. Bowel side effects may be worse in the short term than with a prostatectomy. It may be some time before you and your doctors know if treatment has been successful. If the cancer comes back after radiotherapy, it is more difficult to have a prostatectomy.

Getting support

Macmillan is here to support you. If you would like to talk, you can do the following:

About our information

  • References

    Below is a sample of the sources used in our prostate cancer information. If you would like more information about the sources we use, please contact us at cancerinformationteam@macmillan.org.uk

    C. Parker, E. Castro, K. Fizazi, et al. Prostate cancer: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. Annals of Oncology, 2020, Volume 31, Issue 9, p1119-1134. Available from www.esmo.org/guidelines/genitourinary-cancers/prostate-cancer

    National Institute for Health and Care Excellence (2019) Prostate cancer: diagnosis and management (NICE guideline NG131). Last updated December 2021 to include Risk stratification for localised or locally advanced prostate cancer. Available at www.nice.org.uk/guidance/ng131


  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editors, Dr Jim Barber, Consultant Clinical Oncologist and Dr Ursula McGovern, Consultant Medical Oncologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

The language we use

We want everyone affected by cancer to feel our information is written for them.

We want our information to be as clear as possible. To do this, we try to:

  • use plain English
  • explain medical words
  • use short sentences
  • use illustrations to explain text
  • structure the information clearly
  • make sure important points are clear.

We use gender-inclusive language and talk to our readers as ‘you’ so that everyone feels included. Where clinically necessary we use the terms ‘men’ and ‘women’ or ‘male’ and ‘female’. For example, we do so when talking about parts of the body or mentioning statistics or research about who is affected.

You can read more about how we produce our information here.

Date reviewed

Reviewed: 01 October 2021
Next review: 01 October 2024
Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.