Balancing the benefits: radiation, radiotherapy and cancer risk
The use of radiation to treat cancer – an approach known as radiotherapy – dates back to the early 20th century, when doctors realised that the rays emanating from the radioactive metal radium had the power to kill cancer cells.
Today, around a quarter of all cancer patients in the UK receive radiotherapy as part of their treatment. However, as well as saving lives by treating tumours, stray radiation also has the ability to damage healthy tissue and it can cause side effects ranging from skin damage and fatigue to serious organ damage, depending on the part of the body that has been treated and the dose delivered to the healthy tissue.
To find out how best to use radiotherapy to treat cancer patients while minimising side effects, Professor of Medical Statistics, Sarah Darby, and her team at the NDPH are taking a detailed look at the benefits and risks of radiotherapy.
As an expert number-cruncher, she specialises in bringing together and sifting through large datasets in order to find meaningful results, and her findings are helping to change the way that people are treated for cancer and improve their long-term health, here in the UK and beyond.
Nearly two-thirds of UK women with breast cancer will have radiotherapy as part of their initial treatment, usually treating the area that is left after a tumour has been removed through surgery.
Working together with her NDPH colleagues as part of the Early Breast Cancer Trialists’ Collaborative Group (EBCTCG), Professor Darby analysed data from more than 10,000 women who took part in 17 clinical trials of breast cancer treatment.
Impressively, the results showed that for women who have had a ‘lumpectomy’ (a type of surgery that removes the tumour but leaves the remaining breast tissue behind), radiotherapy halved the chances of their cancer coming back, and cut the chances of dying from it by about a sixth.
However, it’s not all good news. Human anatomy poses a problem, as the heart and lungs lie directly underneath the breasts and are likely to receive some radiation too. Darby has also found that the likelihood of developing coronary heart disease increases depending on how much incidental radiation the heart is exposed to during treatment, especially if a woman already has an increased risk due to other factors such as diabetes or if she is a smoker.
Professor Darby and her team have gathered and analysed huge amounts of data looking at the impact of radiotherapy on other vital organs. For example, they’ve shown that the amount of stray radiotherapy to breast cancer patients’ lungs varies widely around the world, and can be reduced by delivering the radiotherapy only when the patient has taken a deep breath.
They’ve also looked at the risk of side effects in other cancers that are commonly treated with radiotherapy, particularly focusing on Hodgkin lymphoma – a cancer of the immune system that tends to affect children and young adults.
Given that most young people with the disease will live for decades after treatment, it is especially important to understand the long-term risks and side effects of radiotherapy – including the chances of developing a second cancer later in life as a result of radiation exposure – and work out how best to minimise them.
'Delivering radiotherapy more safely is a key objective for our research, and it’s becoming a bigger issue as more and more people are surviving,' says Professor Darby. 'The flip side of this success is that we need both to understand and to quantify the risks for each individual patient in order to balance the need to treat their cancer effectively while avoiding unnecessary side effects.'
As well as researching the risks of radiotherapy for cancer patients, Professor Darby has also been instrumental in investigating how radiation might be involved in causing cancer in the first place – an interest that was first sparked when she spent a year in Japan researching the long-term effects of radiation released from the atomic bombs dropped on Hiroshima and Nagasaki.
Back in the UK, she became curious about the effects of radon, which is a naturally-occurring radioactive gas produced from uranium-rich rocks and soil. Some areas of the UK have relatively high radon levels, especially granite-rich regions like Devon and Cornwall. And although the gas usually disperses into the outdoor air where the radioactivity quickly decays away, concentrations can build up inside enclosed living spaces such as basements and cellars.
Importantly, Darby and her team found that while living in a radon-rich area had a small impact on lung cancer risk for non-smokers, the risks are much greater for people who smoke. In fact, many countries have now changed their building regulations to avoid radon build-up, partly as a result of this finding.
Over the years, Professor Darby and her team have published a large number of papers looking at whether the risk of cancer is increased by a wide range of exposures, including smoking, dental and diagnostic X-rays, atomic weapons testing, living close to a nuclear power plant, and even inhaling spores from bracken plants.
It’s work that is ever more crucial in a world where the media seem only too eager to jump on every new cancer scare and it perfectly sums up the mission of the NDPH, delving into the data in search of answers to some of the most important questions affecting public health.
'We need to bring together all kinds of researchers to do this work,” Darby says. “I’m working with epidemiologists, statisticians, oncologists and medical physicists – there’s still a lot we don’t know, but we’re working hard to find out.'