What is radiotherapy?

Radiotherapy uses high-energy rays to treat disease. It can be given both externally and internally.

  • External radiotherapy aims high-energy x-rays at the affected area using a large machine.
  • Internal radiotherapy involves having radioactive material placed inside the body.

Radiotherapy works by destroying cancer cells in the area that’s being treated. Normal cells can also be damaged by radiotherapy, which may cause side effects. Cancer cells cannot repair themselves after radiotherapy, but normal cells usually can.

You can be given radiotherapy for different reasons. Doctors can give radiotherapy to try and destroy a tumour and cure the cancer. This is called curative treatment. It may be used with other treatments, such as surgery or chemotherapy.

If it’s not possible to cure the cancer, doctors may give you radiotherapy to help relieve symptoms you have. This is called palliative treatment.

The type of radiotherapy you’re given will depend on the type of cancer you have and your individual situation.

What is radiotherapy?

Radiotherapy is the use of high-energy rays, usually x-rays and similar rays (such as electrons) to treat disease. It works by destroying cancer cells in the area that’s treated.

Although normal cells can also be damaged by radiotherapy, they can usually repair themselves, but cancer cells can’t.

Radiotherapy is always carefully planned so that it avoids as much healthy tissue as possible. However, there will always be some healthy tissue that’s affected by the treatment and this will cause side effects.

Radiotherapy explained

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


Ways of giving radiotherapy

There are two ways of giving radiotherapy: external beam radiotherapy (also known as external radiotherapy) and internal radiotherapy.

External radiotherapy is given from outside the body usually using high-energy x-rays.

Internal radiotherapy is given from a radioactive material placed within the body. This may be:

  • a solid radioactive material that is put close to, or inside, the tumour. This is known as brachytherapy.
  • a liquid source of radioactive material called a radioisotope. This is given as an injection into a vein or taken as a liquid or capsule by mouth. This is known as radioisotope therapy or radionuclide therapy.

Whether you have external or internal radiotherapy will depend on the type of cancer you have and where it is in the body. Some cancers are treated with both external and internal radiotherapy.


Why radiotherapy is given

Many people with cancer will have radiotherapy as part of their cancer treatment. Radiotherapy may be given for different reasons.

Curative treatment

This is given with the aim of destroying a tumour and curing the cancer. Curative treatment is also known as radical treatment. Curative treatment may be given on its own, or it may be given before or after surgery or chemotherapy. Chemotherapy is the use of anti-cancer (cytotoxic) drugs to destroy cancer cells.

If radiotherapy and chemotherapy are given at the same time, this treatment is known as chemoradiation.

Palliative treatment

This is given when it’s not possible to cure a cancer. Radiotherapy may be given to relieve symptoms such as pain. Lower doses of radiotherapy are given for palliative treatment than for curative treatment, and they’re usually given over a shorter period of time. Sometimes just a single dose is given.

Radiotherapy treatments are planned on an individual basis. This means that even if someone you’ve met has the same type of cancer as you, their radiotherapy treatment may be different.


Children and radiotherapy

Radiotherapy can be a frightening experience for both children and their parents. Understanding what’s involved can help.

Radiotherapy staff are used to treating children and can offer help and support. A play therapist will often be available as well to provide support.

We have more information about radiotherapy for children.


Back to Radiotherapy explained

Possible side effects

There are things you can do to help manage the possible side effects of radiotherapy treatment.

Who might I meet?

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

After treatment

It can take time for your body to recover after finishing treatment. Advice and support is always available.