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About external radiotherapy

External radiotherapy uses specialised radiotherapy machines to aim radiation beams at a cancer. This destroys the cancer cells. There are many different types of external radiotherapy.

What external beam radiotherapy is

External radiotherapy destroys cancer cells using radiation from a machine. The most common types of external radiotherapy use high energy x-ray beams, such as photon beams. 

Other types of radiotherapy include particle beams, such as protons or electrons. The radiotherapy beams destroy the cancer cells in the treatment area.

How radiotherapy works

Radiotherapy treatment works by damaging the DNA within the cancer cells. DNA is the genetic code that controls how the body's cells behave. 

The radiotherapy either damages DNA directly or creates charged particles called free radicals that damage the DNA. Then the cancer cells stop growing or die. When the cells die the body breaks them down and gets rid of any waste substances. Normal cells in the radiotherapy area might also be damaged but they can usually repair themselves.

Before starting your treatment

Before starting your treatment your doctor will discuss with you the possible short term and long term side effects. Most side effects are temporary and can usually be well controlled with medicines.

Your treatment team uses images from a range of tests to plan and monitor your treatment. The tests might include x-rays, CT scans, MRI scans, or PET scans. Your treatment team plans the radiotherapy to give a high dose to the cancer. 

How you have external radiotherapy

You have treatment in the radiotherapy department. Radiotherapy machines are very big and they vary slightly in how they look and how they work.

Photo of a linear accelerator
A photograph of a linear accelerator

The most common type of machine is called a linear accelerator machine (LINAC), which uses electricity to create the radiotherapy beams.

The machine doesn't touch you and you don’t feel anything during treatment. But you may get some discomfort or pain later on from the side effects. 

For the radiotherapy to work as well as possible, it is important that the radiotherapy field covers the whole cancer, plus a border around it.

Doctors try to give as low a dose as possible to the surrounding healthy tissue to reduce the risk of side effects.

Radiotherapy fractions

The full dose of radiation is usually divided into a number of smaller doses called fractions. This allows healthy cells to recover between treatments. You have the fractions as a series of treatment sessions that make up your radiotherapy course.

Radiotherapy to relieve cancer symptoms, such as pain, is called palliative radiotherapy. You often have this in fewer fractions and sometimes it is just one treatment. The radiotherapy dose with each fraction is bigger but you have fewer fractions so the overall radiotherapy dose is lower.

Palliative radiotherapy has fewer side effects than radiotherapy that aims to cure the cancer.

Your course of treatment

When deciding on your course of treatment your radiotherapy doctor takes into account:

  • your type of cancer
  • the position of the cancer in the body
  • any other treatment you've had, are having, or is planned for you
  • your general health and fitness

This means that your treatment will be individual to you.

A course of radiotherapy aimed at curing cancer usually lasts between 1 to 6 weeks but may be longer than this. Your doctor will tell you how long your treatment will take.

Many people have daily treatment from Monday to Friday, with a rest at weekends. Others have different treatment plans, such as 3 days a week, or treatment 2 to 3 times a day, including at weekends. The radiotherapy staff try to give you appointments for the same time each day so that you can get into a routine.

Types of external radiotherapy

Your doctor chooses the type of radiotherapy and the machine for your treatment according to the type of cancer you have and where it is in your body. There are different types of external radiotherapy treatment, which include

  • conformal radiotherapy
  • intensity modulated radiotherapy (IMRT)
  • image guided radiotherapy (IGRT)
  • 4-dimensional radiotherapy (4D-RT)
  • stereotactic radiotherapy and radiosurgery
  • proton therapy
  • electron beam radiotherapy
  • adaptive radiotherapy

Effects of radiotherapy

External radiotherapy doesn't make you radioactive. It is safe to be with other people, including children, throughout your treatment.

People react to radiotherapy in different ways:

  • some carry on working and just take time off for their treatment
  • others feel tired and want to stay at home
  • some people stay in hospital for all or part of the treatment

Your doctors, radiographers and nurses will advise you about how best to manage your course of treatment. If you have family members to look after, you may need extra help. You can ask for help from your employer, family or friends, or the staff in the radiotherapy department. 

As your treatment goes on you'll have more idea of how it makes you feel. You can then make any necessary changes to your daily life to help you cope with the rest of your treatment course.

Last reviewed: 
15 Feb 2016
  • External Beam Therapy
    Peter Hoskin
    OUP Oxford, 30 Aug 2012

  • De Vita, Hellman, and Rosenberg's Cancer: Principles and Practice of Oncology (9th edition)
    De Vita, V.T., Lawrence, T.S. and Rosenberg S.A.
    Lippincott, Williams and Wilkins, 2011

  • Radiotherapy Services in England 2012. 
    Department of Health, November 2012.

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