Radiotherapy uses ionising radiation to treat cancers. Three types of radiations are used: gamma, beta and X-rays. The radiation is concentrated onto the site of the tumour to damage the chromosomes in the rapidly-growing cancer cells which destroys them.

There are two main types of treatment - external and internal radiotherapy.

In this treatment, a beam of ionising radiation is aimed at the cancerous growth. The source of the beam is moved around. In this way, the beam is always focused on the tumour but doesn't take the same route through healthy tissue. The tumour gets a high dose, whilst the surrounding healthy tissue gets a lower dose.

External radiotherapy uses X-rays and sometimes gamma rays. Exposure to the x-rays can vary depending on the dose required to treat the cancer and a session would typically last about 15 minutes. This would be repeated daily for up to six weeks, usually with breaks at the weekend to reduce damage to healthy cells and allow the patient to recover from the treatment.

The X-rays can be produced by a machine that is similar to those used for taking images of broken bones. The energy of the X-rays can be varied and is usually much higher than that of imaging X-rays. This higher energy makes them more penetrative and more ionising.

Low and medium energy X-rays are particularly suitable for treating cancers on the outside of the body. To reach internal tumours requires very high energy radiation.

This can be produced by super high voltage machines but sometimes, a radioactive source such as cobalt-60 or iridium-137 is used. When they decay, these radioactive sources produce high energy X-rays and gamma (which are even higher energy). These radiations are more penetrating and are therefore more suitable for internal tumours.

The patient does not come into contact with any radioactive sources and does not become radioactive as a result of the treatment.

Cancers of the cervix, womb, neck, prostate gland or the skin are often treated using radio active sources that are positioned close to the tumour. This can be in the form of a small capsule which is placed near the tumour or on the surface of the skin. Sometimes a radio active liquid may be injected into a vein. The patient carries the source inside them, so they normally need to stay in hospital while it is in place.

These types of radiotherapy usually use a source of beta radiation like technetium-99. Beta radiation is short range so its effects are very localised. This means that a higher dose can be given with less damage to surrounding tissues.