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This entry is part 2 of 2 in the series Radiotherapy

Part two of our new blog series on radiotherapy delves into the subject of proton beam therapy. We cover how this treatment works, whether it’s worth the hype, and the latest developments in the UK’s proton beam therapy service.

Given the amount of media attention that proton beam therapy has received in recent years, it’s not surprising that so many people are familiar with this treatment. But what some might not know is that proton beam therapy is, in fact, a kind of radiotherapy, albeit a relatively new one.

Behind the buzz is the fact that proton beam therapy is very precise, making it well suited to tackling certain cancers where treatment can be tricky, such as in children. So it is exciting that the UK will soon be equipped with its own state-of-the-art centres and treating patients from next year.

Is this the start of a revolution in cancer treatment in the UK, as many headlines have promised? Or has the potential of proton beam therapy been over-stretched, leading to false hopes of what it can offer? We caught up with experts in the field to find out what this kind of treatment really could mean for cancer patients in the UK.

Protons and photons: spot the difference

As discussed in the previous post, despite being around for well over a century radiotherapy remains a cornerstone treatment for cancer. It works by aiming high doses of radiation precisely towards a person’s tumour, either from inside the body or outside, which damages the cancer cells’ DNA and causes them to die.

Although different forms of radiotherapy use different types of radiation, they all work in this way. The most commonly used type are x-rays, teeny packages of light – or photons – that are launched at the tumour in highly-targeted beams. Modern radiotherapy techniques, such as conformal radiotherapy, use imaging techniques to carefully plan the treatment in 3D so that the x-rays are closely moulded to the shape of the tumour.

The problem is that no matter how accurate the beams are, x-rays give off potentially damaging energy as they enter the body and keep going once they’ve hit their target, albeit losing energy as they go. Since the radiation can’t distinguish a healthy cell from a cancer cell, this means that there is a risk of damaging healthy tissue around the tumour, causing side effects.

Protons on the other hand are tiny particles found within the hearts of atoms. They behave differently to the more energetic x-rays, in a way that makes them very attractive as a treatment. The key difference is that when the protons reach their carefully mapped out target, they come to a grinding halt. Here, they deliver a powerful burst of radiation on the spot, hitting the tumour precisely where it hurts.

“This is one of the main reasons that protons are thought to have an advantage over x-rays,” explains Professor Karen Kirkby, Professor of Proton Therapy Physics at the University of Manchester and The Christie Hospital.

“With protons a very high dose is delivered right at the tumour, then there is a sharp cut-off where the dose drops right down. So the idea is that you can use this type of radiotherapy close to fragile organs and lower the risk of damaging them.”

On top of that, Kirkby says, the overall dose of radiation given to the healthy tissue in proton beam therapy is lower than with conventional radiotherapy, another desirable feature when weighing up the potential risks.

Protons, what are they good for?

Conventional radiotherapy is a very effective treatment for many cancers, but there are some situations where the unique properties of protons make them an obvious choice over x-rays.

Children, for example, are still growing and therefore vulnerable to potential long-term side effects from radiation exposure, such as growth problems and developing treatment-related cancers later in life.

“That’s why proton beam therapy is approved in the UK for many children’s cancers, where it’s critical not to give high doses to the tissue around the tumour,” says Professor Gillies McKenna, director of our Oxford Institute for Radiation Oncology.

“And if you look at adult cases that are also approved for proton beam therapy, for example tumours next to the spinal cord or brain stem, for most that’s also the main consideration.”

For these patients, where proton beam therapy offers a clear advantage over conventional radiotherapy, the NHS pays for treatment abroad in already established centres in the US and Switzerland, and has been doing so since 2008. That does not come cheap. The cost of the therapy, transport and care abroad – for patients and their families – soon racks up a large bill for the NHS. Not only that, but some patients simply aren’t well enough to travel that far; it’s a huge toll on their already fragile bodies.

That’s why, in 2009, the UK government made the decision to set up a National NHS Proton Beam Therapy Service, so that patients could be treated closer to home. Thanks to a £250 million commitment from the government, two centres are under construction: one at The Christie Hospital in Manchester, and one at University College London Hospital.

These new centres will both offer a kind of proton beam therapy known as ‘high-energy’. The UK has been treating patients with another type, known as ‘low-energy’, since 1989. This service at The Clatterbridge Cancer Centre treats people with a rare kind of eye cancer and has saved many from having to have their eyes removed to treat the disease.

Once up and running in Manchester, the first patients will be treated with the high-energy machine from summer next year. London will be offering the therapy two years later due to the significant logistical challenges that building in London has presented. Bringing in the 90-tonne cyclotron – the machine that generates the protons – is only part of the immense construction battle, not to mention digging the 32-metre hole to house the equipment and the metres of concrete walls needed to encase it.

“Once both Centres are open, the total number of patients expected to be treated each year is 1,500,” Kirkby says.

“That may sound small, but these are patients with complex cancers where we know conventional radiotherapy is difficult, and there’s some evidence that they’ll do better with proton beam therapy.”

Is proton therapy truly a revolution?

So if proton beam therapy seemingly has advantages over conventional radiotherapy, why isn’t it being offered to more patients in the UK? The situation isn’t so black and white.

Researchers have been developing and refining conventional radiotherapy for many decades, but proton beam therapy hasn’t been around for as long. That means we don’t yet have the same strong evidence base for this treatment to show which cancers it could offer benefits for, and few long-term clinical studies to look for side effects later in life.

“The long-term patient data that’s coming out now is from patients treated with proton beam therapy technology from 20 years ago,” says Kirkby. “It’s therefore not representative of the state of the art technology we have available today, so it will not reflect what we can do for patients now.

“The UK is also very evidence-driven, and currently there isn’t a huge amount of evidence, at the moment, that protons give better outcomes than conventional radiotherapy.”

McKenna echoes this point: “At the moment there isn’t any evidence that protons are more or less effective than x-rays at treating cancer.”

“At the moment there isn’t any evidence that protons are more or less effective than x-rays at treating cancer”

– Professor Gillies McKenna, Oxford University

Experts argue that we need more clinical and scientific data, because while conventional radiotherapy and proton beam therapy are both variations of the same type of treatment, that doesn’t mean they should be regarded as equivalents where the science and treatment approaches are transferrable.

Cost is another consideration. At the moment proton beam therapy treatment is much more expensive than x-ray therapy. For many cancers, we know that conventional radiotherapy can be very successful and even curative. So the issue, McKenna argues, is not whether proton beam therapy is going to be as effective, but whether the patient benefit is enough to justify the extra cost.

In some situations this is clear-cut, where the tumours are near vital organs. But at the moment for many other cases where radiotherapy is suitable, there just isn’t enough evidence that protons can offer significant benefits over x-rays, which we know are effective. That said, as more patients are treated and more research is carried out, it’s possible that proton beam therapy may emerge as a better option for other cancers that currently aren’t on the NHS list. That’s the beauty of research. And of course, with the development of any technology comes a gradual drop in price.

“If we look at most of the progress and developments in radiotherapy over the last 30 years, it’s not so much that we’ve discovered ways to make radiation more effective; we’ve worked on ways to make it safer,” says McKenna.

“Proton beam therapy is another step change in how we do that.”

What else do we need to know, and what’s the UK doing about that?

As proton beam therapy is still relatively new, there are some important grey areas that need to be resolved through research. One of these, Kirkby says, is the question of where exactly the protons go in patients.

“X-rays travel through the body and can be picked up when they exit, meaning that we can also use them to image the patient during treatment,” she adds.

“But protons stop inside the body. So the big question is: can we work out precisely where this happens in each patient?” That’s a crucial piece of missing information, since the end of their journey is where they release a big dose of radiation. While this is arguably the greatest asset of protons, it also adds another layer of complexity. If a patient moves, there is a risk of giving healthy tissue a large amount of radiation.

Accurate scanning techniques have been developed to help reduce this risk, which the UK centres will be equipped with. Kirkby’s team is also working on ways to better predict the journey that protons will take in patients to make the treatment even more precise.

Another area we need to know more about, says McKenna, is how best to combine protons with other treatments, such as targeted drugs and immunotherapies.

“At the moment we don’t know whether x-rays and protons will act in the same way in these situations,” he adds.

By strategically nestling the two new UK Centres within world-renowned academic hubs, research and trials into fundamental areas such as this can be carried out alongside treating patients, which will speed up progress and clinical development of the field. That could mean that proton beam therapy opens up to more patients in the UK in the future, if the evidence stacks in its favour.

Ultimately, that doesn’t mean the treatment will be more likely to cure their disease than conventional radiotherapy. But it may be a safer way to deliver the therapy. And since we need to make treatments kinder, as well as more effective, then it’s potentially an important new tool to help improve the outlook for people with cancer.

Justine

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