What is external radiotherapy?

External radiotherapy uses a machine from outside of the body. It directs radiation beams at the cancer to destroy it.

This is different to internal radiotherapy which means giving radiotherapy to the cancer from inside the body.

Go to our information on internal radiotherapy

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.

Before starting your treatment

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

Your treatment team uses images from scans and x-rays to plan your treatment. You might have a:

• CT scan

• MRI scan

• PET scan

• x-ray

Your treatment team carefully plans the radiotherapy to give a high dose to the cancer. While sparing as much healthy tissue as possible. 

Read more about planning for external radiotherapy

External radiotherapy equipment

There are many different types of radiotherapy equipment. The most common radiotherapy machine is a Linear Accelerator (LINAC).

The type of radiotherapy machine that you have your treatment with depends on:

• where your cancer is

• whether your cancer is near the skin surface or not

• whether it has spread

• the type of cancer

Most radiotherapy machines are very big. This means they are often in large rooms.  

Some radiotherapy machines can also take x-rays. This checks that you are in the same position as your planning scan for your treatment. You may have x-rays before your treatment but it depends on where your cancer is. For example, your radiographer won't take x-rays for treatment of skin cancer. This is because they can clearly see where they need to treat.

It's normal to feel anxious about radiotherapy treatment. But as you get to know the staff and the procedure, it usually gets easier. Don't be afraid to talk to the staff about any fears or worries. They are there to help you.

How you have external radiotherapy

You have treatment in the radiotherapy or proton therapy department. Radiotherapy machines are very big and can vary in how they look and work.

The most common type of machine is a linear accelerator (LINAC). It uses electricity to create the radiotherapy beams. You will hear the buzzing sound of the machine as it switches on. 

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. These are called fractions. This allows healthy cells to recover between treatments. You have the fractions as a series of treatment sessions. This makes up your radiotherapy course. You might have a course of treatment over several weeks, but this varies.

Sometimes your radiotherapy treatment might have different courses or phases. For example, in a second phase of treatment you may have radiotherapy to a smaller area compared to the first phase of treatment. So, the second phase area gets an extra dose. Or occasionally you may have different types of radiotherapy in different phases of treatment. This depends on several things including:

• the type of cancer you have

• where it is

• other types of treatment you might be having

Your doctor or radiographer will let you know if you need more than one course or phase of treatment.

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

Types of external radiotherapy

Most types of radiotherapy treatments use photons such as x-rays. But tiny particles called electrons and protons can also be used.

Photons and protons can treat cancers that are deep inside the body. Or those on or close to the skin (superficial cancers). Electrons are only used for superficial cancers. 

Treatments using photons, protons and electrons will vary slightly. But the experience of having radiotherapy will be similar.

Your doctor chooses the type of radiotherapy and the machine for your treatment. This depends on the type of cancer you have and where it is in your body. There are different types of external radiotherapy treatment. They include:

• conformal radiotherapy

• intensity modulated radiotherapy (IMRT)

• image guided radiotherapy (IGRT)

• 4-dimensional radiotherapy (4D-RT)

• stereotactic radiotherapy (SABR) and radiosurgery (SRS)

• adaptive radiotherapy

Find out more about the different types of external radiotherapy

Side effects of radiotherapy

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

Side effects vary depending on which part of the body is being treated. And if you are having radiotherapy with other treatments, such as chemotherapy. General short term side effects include:

• tiredness

• sore skin 

• hair loss in the treatment area

People react to radiotherapy in different ways:

• some carry on working and only 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 radiotherapy team 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 of an 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.

Find out more about the side effects of radiotherapy