External-beam radiotherapy

External beam radiotherapy is planned by an oncologist, a doctor who specialises in cancer treatments. You will need to visit the hospital once or twice so your treatment can be planned.

As part of your planning you will have a CT scan, which takes x-rays to build up an image of your body. There may be some preparation you need to do before the scan such as following a special diet and having an enema. This is to make sure the pictures are as clear as possible. The hospital staff will tell you what preparation is needed.

Some men may have small very small gold grains put into their prostate gland. These act as markers for the radiographers as the position of your prostate varies slightly from day-to-day.

At the beginning of each radiotherapy session your radiographer will position you carefully then leave you alone in the room. The treatment isn’t painful but you do have to lie still for a few minutes.

The main ways of giving external-beam radiotherapy are conformal and intensity-modulated radiotherapy (IMRT).

External beam radiotherapy

External-beam radiotherapy treats cancer by using high-energy x-rays to destroy cancer cells, while doing as little damage as possible to normal cells. It’s the most common way of giving radiotherapy for locally-advanced prostate cancer. It is usually given with hormonal therapy.

The treatment is given in the hospital radiotherapy department. It’s usually given as daily sessions from Monday–Friday, with a rest at the weekend. The course of treatment may take up to eight weeks.

Planning external radiotherapy

External beam radiotherapy is planned by an oncologist. Planning is a very important part of radiotherapy and may take one or two visits to hospital. The treatment is carefully planned to make sure it is as effective as possible. 

As part of your planning, you’ll be asked to have a CT scan, which takes x-rays of the area to be treated.

Before your CT scan you may need to follow a special diet. Occasionally, you may be asked to have an enema. This involves having a small amount of liquid passed into your rectum through a thin tube. The liquid will help you to empty your bowel before the CT images are taken. Having an empty bowel gives very clear CT images and this helps your radiographers plan your treatment.

Just before the scan you may also be asked to drink a few glasses of water to fill up your bladder. This will also help to give clear CT images. If you need to follow a special diet, have an enema or drink fluids before your scan, you will be given written information about this.

During your planning tiny tattoos or permanent marks may be drawn on your skin. These show where the radiotherapy is to be given. They help the radiographers position you accurately and set up where the treatment will be given.

The marks are usually permanent. They are the size of pinpoints and will only be done with your permission. Having the tattoos done can cause some discomfort but this won’t last long.

Some men may have very small gold grains put into their prostate gland during an outpatient procedure. The prostate gland moves when you breathe or when your bowel is full. The gold grains act as markers to help your oncologists plan each of your daily treatments accurately. This helps to reduce side effects and damage to organs that are close to the prostate gland.

There are other ways of planning your treatment accurately. Your hospital team can tell you more about the techniques they use.

Radiotherapy can make your skin sore. During your planning appointments you’ll be given advice about how to look after your skin.

Radiotherapy explained

Consultant Clinical Oncologist Vincent Khoo describes external beam radiotherapy, how it works, and what it involves.

Information about our videos

Radiotherapy explained

Consultant Clinical Oncologist Vincent Khoo describes external beam radiotherapy, how it works, and what it involves.

Information about our videos

Treatment sessions

At the beginning of each session, the radiographer positions you carefully on the couch and makes sure you are comfortable. You will be alone in the room during treatment. But you can talk to the radiographer who is watching from the next room. Radiotherapy is not painful, but you need to lie still for a few minutes while it’s given.

My radiotherapy was a strange experience since in spite of lying on a couch under an impressive whizzing machine behind thick doors, I felt absolutely nothing.


Advantages of external-beam radiotherapy

  • It may lead to a cure for some men. For others it will help control the cancer for many years.
  • Giving hormonal therapy before, during and/or after radiotherapy may improve the results.


  • For a small number of men it can cause long-term bowel problems, such as loose or more frequent bowel motions, bleeding from the back passage or an altered bowel pattern.
  • A small number of men will develop urinary incontinence.
  • Some men will develop erection problems and infertility.

Ways of giving external-beam radiotherapy

There are different ways of giving external radiotherapy. All the current ways of giving radiotherapy aim to reduce damage to healthy tissues and side effects.

Conformal radiotherapy uses a device inside the radiotherapy machine to shape the radiation beams to fit the treatment area.

Intensity-modulated radiotherapy (IMRT) shapes the radiotherapy beam more than conformal radiotherapy. It allows different doses of radiotherapy to be given to different parts of the treatment area. A TomoTherapy® machine combines IMRT with a CT scan so each treatment is very accurate.

Your cancer specialist can tell you more about the type of radiotherapy you are having.

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Who might I meet?

You will meet many different specialists before, during and after radiotherapy treatment.