An introduction to radiotherapy: what is it, how does it work, and what’s it for?

In the first instalment of our new blog series on radiotherapy, we give a broad overview of this type of treatment for cancer, tracing back to its roots in the 19th Century to how it’s used today.

It’s been used in cancer medicine for more than a century, but radiotherapy is far from old-fashioned. Thanks to decades of research to refine, improve and innovate the treatment, it’s become an incredibly sophisticated and precise technique that cures more people than cancer drugs. In England alone, around 134,000 courses of radiotherapy are given each year. So how did this cornerstone treatment that’s helped save millions of lives come about?

The story begins in November 1895, when German physicist Wilhelm Rontgen was busy experimenting with the effects of electricity on gases. Little did he know that he would happen upon something that would make its way into hospitals across the world virtually in the blink of an eye: the x-ray.

With a helping hand from his wife (quite literally), Rontgen showed that the mysterious new type of radiation he had discovered could travel through certain substances, such as flesh, but was blocked by others, like bones.

This discovery soon ushered a new era of medical imaging, known as radiology, helping doctors identify fractures and other previously invisible maladies. It was during this surge of worldwide interest into x-rays that scientists made another crucial observation: x-rays could damage the skin if used repeatedly. This prompted scientists to wonder whether they could take advantage of this effect to treat disease, including cancer.

Early work in the lab and on people supported this idea and soon, thanks to the legendary scientific duo Marie and Pierre Curie, another type of radiation joined the medical scene: radium. Realising the potential of this new and exciting treatment, in the 1920s we raised large sums of money to buy radium for research, starting with the treatment of cervical cancer.

Our scientists then continued to carry out pioneering research on radiotherapy, working out how to measure doses and showing how cells respond to radiation, among many other crucial studies. Ultimately, this work laid the foundations for modern radiotherapy, which has dramatically improved since its inception.

• Watch an animation explaining how radiotherapy works

So, how does it work?

Radiotherapy works by aiming a high dose of radiation towards a person’s tumour, which damages cells’ fragile DNA – the code of instructions that cells need to survive and do their job.

This can happen in two ways. The radiation can directly damage the DNA by causing breaks along the strands of genetic material, and it can also trigger the formation of very reactive molecules that themselves can be damaging. Unable to cope with this assault to their lifeline, ultimately the cancer cells die.

Radiation can fracture strands of DNA

Since the radiation has to travel through healthy tissues to reach its target, non-cancerous cells may too become damaged by the treatment. Cells have their own tools to fix damage to DNA as it arises, but in cancer cells these are often faulty. So while healthy cells are usually able to stitch their DNA back together and avoid the fatal consequences of the radiation, cancer cells can’t.

That’s why radiotherapy is given to patients across a number of sessions that are spread out over time – these gaps allow the healthy cells to recover. Any harm to healthy tissues is a potential risk though and can lead to side effects. Reducing this risk is crucial to making the treatment kinder for patients, and why modern radiotherapy techniques aim to minimise this collateral damage while also maximising the dose that the tumour gets.

Beams, wires and drinks

Over the years, scientists have come up with a number of ways to make radiotherapy more elegant and precise, but in principle the treatment remains the same: a high dose of radiation aimed at the tumour. Although there are many types, broadly radiotherapy is given in 2 ways, from either outside the body (external radiotherapy) or inside (internal radiotherapy). Not everyone has radiotherapy as part of their treatment, but which one is used depends on the type of tumour and where it is in the body, among other things.

For example, a type of internal radiotherapy called radioactive iodine therapy is a very effective treatment for patients with thyroid cancer. The radioactive iodine is given as a drink or in a pill and is then taken up by the thyroid cancer cells, but not healthy cells, and hence has few side effects. This is known as radioactive liquid therapy and is one of two main types of internal radiotherapy. The other, called brachytherapy, involves placing a radioactive implant next to the tumour, such as tiny metal pellets or wires.

Although internal radiotherapy works well for certain cancers, external radiotherapy is the most common type used. Different kinds of radiation are used here, usually x-rays but sometimes tiny particles like protons which are found in the hearts of atoms. The radiation is hurled toward the tumour in beams ejected from a highly sophisticated machine, most commonly one called a linear accelerator.

Rather than relying on a degree of guesswork like in the very early days of radiotherapy, today doctors take very detailed images of patients’ tumours and their surroundings using techniques like CT or MRI scans. This helps doctors plan the treatment very precisely in 3D, so the tumour bears the brunt of the blow while its neighbouring healthy tissues are spared as much as possible.

There are also a variety of other tricks to make the treatment more accurate, such as aiming the beams from a number of angles so that they can closely shape the tumour, or switching up their intensity. You’ll hear more about these techniques in the posts that follow in this series.

Old but gold

Although radiotherapy has dramatically improved and modernised over the years, as with any treatment it’s not perfect and still has issues. The main problem is that even with targeted radiotherapy, it’s very difficult to leave healthy tissue around the cancer completely unharmed. Beams of radiation both enter and exit the body through healthy tissue, and tiny movements by the patient and even breathing can put the tumour slightly off target, leading to side effects from damaged healthy tissue.

This is a particular issue for children and young people, whose delicate and growing bodies are particularly susceptible to these off-target effects. Such patients have a risk of developing another cancer later in life as a result of the therapy, which is why doctors must weigh up the benefits with the risks while planning their treatment. Proton beam therapy, a highly-targeted type of radiotherapy that has shown promise in these more complex cases, may reduce these risks – a topic we’ll be covering in depth in the next post.

So while there are still improvements to be made, radiotherapy may be old, but it’s gold: It’s been helping patients survive cancer for well over 100 years and continues to be one of the most important tools that cancer doctors have. As with any treatment it carries risks, both short- and long-term. But as the technology continues to improve, so too will these be minimised, helping patients live longer, healthier lives.

Justine