Radiotherapy for cancer - everything you need to know

16th May 2023

Radiotherapy is one of the UK’s most commonly used cancer treatments. You’ve probably heard of radiotherapy; you might even know someone who has had radiotherapy. But what is radiotherapy, how does it work, and how is research making radiotherapy better, and kinder?

What is radiotherapy?

Radiotherapy is a form of cancer treatment that uses ionising radiation to target cancer cells. Ionising radiation is a very high-intensity type of energy that is released from tiny particles called atoms. It has the power to damage the DNA in cancer cells, and it can be used to shrink tumours or to clear up any cancer cells that might have spread.

Around 100,000 courses of radiotherapy for cancer were given in England in 2020. Radiotherapy is sometimes the only treatment a patient receives, but more commonly, patients will receive radiotherapy in combination with other treatments like surgery or chemotherapy.

Whether radiotherapy is used to treat a patient’s cancer or not can depend on a number of different factors, including the type and stage of cancer, and the patient’s health and personal preferences.


What types of radiotherapy are there?

There are currently many different types of radiotherapy, and options are continuously expanding as research improves the way we can direct and deliver radiotherapy treatment.

External radiotherapy is when large machines are used to direct beams of radiation into the cancer in your body.

Types of external radiotherapy:

3D conformal radiotherapy

This is a common form of external radiotherapy where the radiation beams are targeted very closely to the shape of the cancer.

Intensity modulated radiotherapy

This is a type of 3D conformal radiotherapy that can also vary the dose of radiation delivered to the tumour and surrounding healthy cells.

Stereotactic radiotherapy

Delivers radiation beams to the tumour from different angles. This is another way of precisely targeting cancer, while helping to spare healthy cells.

External radiotherapy is usually given in small doses over a period of time with short rest breaks in between. A typical course of radiotherapy might last several weeks, with weekend rest breaks. This helps to make sure that healthy cells have time to recover during the rest periods, while cancer cells gradually accumulate damage and die off over the treatment period.

Internal radiotherapy is when a small amount of radioactive substance is positioned inside the body, usually close to the cancer. The radiation from the substance is enough to kill the cancer cells without penetrating very far into healthy tissue.

Types of internal radiotherapy


Involves placing a tiny solid piece of radioactive substance (called a ‘seed’ or ‘implant’) close to the tumour. The substance may be removed after a short while, or it is sometimes left there permanently. The seed is harmless and will lose its radioactivity over time.

Radioisotope or radionuclide therapy

Involves infusing or drinking a liquid radioactive substance that is then taken up by the cancer cells.

How does radiotherapy kill cancer?

Because ionising radiation is a very strong form of energy, it can cause extensive damage to the DNA in our cells. The radiation causes ‘double-stranded breaks’ in the DNA, and whole sections are snapped completely in two. Cancer cells find this type of damage very hard to repair and they either stop dividing, or they die. Healthy cells are better at repairing DNA and so tend to be more resilient to radiotherapy.

However, healthy cells can still be harmed by the radiation, and this is why a lot of care is taken during radiotherapy treatment to find the right treatment schedule, dosing, and positioning. These factors can all help to make sure that the radiotherapy destroys the cancer as much as possible, while avoiding healthy cells.  

Radiotherapy also tends to have more impact on cells that are dividing quickly. As cancer cells divide very quickly, this is another way that radiotherapy can target cancer cells, while helping to spare healthy cells.

Why does radiotherapy cause side-effects

Side-effects are usually localised to the area where the radiation therapy has been given, and are linked to radiation effects on healthy cells. Because radiotherapy has greater impact on cells which are dividing quickly, it can also affect fast-dividing healthy cells such as those that line the gut. This is why radiotherapy can cause side-effects like diarrhoea.

Does radiotherapy make you radioactive?

External radiotherapy, which involves passing beams of radiation through you, does not make you radioactive.

However, some forms of internal radiotherapy, which can involve using a radioactive substance to target cancer inside the body, may make you radioactive for a short time after the therapy. It is possible that you may need follow some safety precautions to protect others during this time. For example, you might be asked to temporarily keep apart from family and friends. This can be a particularly tough part of the treatment, but it is needed to keep others safe from possible exposure to radiation.


Why are masks sometimes used in radiotherapy treatment?

Radiotherapy must be given very precisely, and different methods are sometimes used to help make sure that the beam is targeted as accurately as possible. Marks and tiny tattoos on the skin can help to make sure the beam is in the right place, and masks and moulds made of mesh are sometimes used to help keep the area of the body still. This helps to ensure the radiotherapy hits exactly the same spot during every treatment session.

How is research improving radiotherapy treatments for people with cancer?

Radiotherapy has been around for over 100 years and thanks to research, huge advances have been made in that time. Sophisticated machines can now target tumours and cancer cells more accurately than ever before- helping to improve effectiveness and reducing side-effects. CT-scans can help direct radiotherapy, and machines called dynamic multi-leaf collimators use moving blocks to precisely shape radiotherapy delivery to the tumour.

Much radiotherapy research is focussed on finding the safest and most effective way to deliver radiotherapy for different cancers. Shorter courses of radiotherapy at higher doses, or even one single session of radiotherapy are now sometimes used to treat some cancers. And the research doesn’t stop there. Radiotherapy is not an option for some people, and some cancers can develop resistance. But vital support from our Curestarters is helping to fix that.

Thanks to you

Your funding has already helped researchers in Spain make potentially life-saving breakthroughs that could one day help doctors identify who will benefit from radiotherapy most, and help to make radiotherapy more effective for patients whose cancer is resistant to treatment. 

And with your help, Dr Perry and her team in New Zealand are working to push forward development of a new type of anticancer drug that could ultimately benefit patients undergoing radiotherapy by helping to make their cancers more sensitive to treatment.



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