It would mean shorter and more effective courses of treatment, generally resulting in more comfort and a better outcome for the majority of patients. It will enable us, longer term, to tackle some major cancers that are not possible to tackle effectively at the moment.
Professor Nigel Allinson
The University of Lincoln are leading a team in advancing more effective radiotherapy treatment with the help of a £1.6 million Wellcome Trust Translation Award. The three year Pravda project will combine imaging techniques developed at Lincoln with detectors produced at the University of Liverpool to establish safer and more accurate proton therapy.
In conventional radiotherapy using high energy X-rays or gamma rays the energy is absorbed into tissue exponentially with distance into the tissue. One of the main disadvantages is the collateral damage that this inevitably inflicts on surrounding tissue, which is why the beam of radiation is moved around to focus on the tumour site. Even so, significant radiation can reach healthy tissue, more so if the tumour site is small or very deep inside the body.
Theoretically, proton therapy has considerable advantages for tackling such tumours, and it is already being put to use at more than 30 sites worldwide. Currently around 400 NHS patients travel abroad to receive proton therapy, but it is hoped that this could all change with the government approving the construction of two treatment centres in the UK.
Professor Nigel Allinson, Distinguished Professor of Image Engineering at the University of Lincoln, has described the ability to image the interaction between radiation and tumour in three dimensions as ‘the holy grail of radiotherapy’. I had the opportunity to quiz him about the Pravda project and started by asking about the advantages of proton therapy over conventional radiotherapy.
"Protons, as particles, behave differently in the way they lose their energy as they pass through tissue," he began. "They lose very little energy until they reach a peak – the Bragg Peak – which you can tune and which is proportional to how fast the protons have been accelerated. You can tune this peak so that, if the tumour site is 10 or 20 cm into the body, you can ensure that 80 per cent or more of the beam is deposited there. You can tune the width of it as well, and still have the capacity to move the beam around to reduce collateral damage.
"Because you can focus the energy into a very small volume, it’s useful for treating tumours near critical organs, along the spinal cord, on the optic nerve or anywhere else in the head and neck."
These strengths stem from the ability of proton therapy to focus a large amount of energy in a very small volume deep inside the body. Administering radiation will always come with some degree of risk, but proton therapy has certain advantages over conventional radiotherapy.
"All radiotherapy increases the chance of developing secondary cancers in the long term. In a 60 or 70 year old patient having treatment for a tumour, there’s not much additional risk involved in terms of developing secondary cancer 20 or 30 years down the line. With young people, however, one has to take special care. The advantages of proton therapy, therefore, are often greater for young people because there’s much less chance of developing a secondary cancer."
According to Professor Allinson, the technology being developed should eliminate the most serious risks attendant in proton therapy.
"The disadvantage is that if you get it wrong, the repercussions are very serious. That’s why you need the instrumentation that we’re going to develop; to ensure that you can monitor before and during treatment exactly where the protons are losing their energy."
Detailed X-ray radiography remains the best means of determining the exact size and location of a tumour beforehand, but the new instruments will measure the profile, distribution and energy of the proton beam before as well as during treatment.
"We know where each particle came from, how much energy it started with, and hence can say how much energy has been lost in the body and where it has interacted with tissue," Professor Allinson explained. "In this way you can build up a 3D picture, just as is done through X-ray computed tomography (CT), to make an exact dose map of where the protons interacted with the body and how much energy was absorbed."
When you have a tumour you want to make sure you treat all of it, but how far do you cut into - or project an energy beam into – healthy tissue? It is important that the margins of uncertainty are as small as possible in cancer treatment.
"If you have a large margin of uncertainty you take out more healthy tissue, and if you don’t take out enough you leave cancer cells and run the risk of a secondary cancer," said Professor Allinson. "We want to reduce this margin of uncertainty from typically about 1 cm down to 2 mm, which may not seem a lot but makes all the difference as to whether you can tackle a tumour which is next to the spinal cord, for example."
It is hoped that in the long-term the prospect of using proton therapy to tackle cancer of the lungs and other common cancers which don’t respond well to radiotherapy will become a reality. In the UK alone approximately 42,000 cases of lung cancer are diagnosed each year, some of which could in future be addressed using proton therapy.
"The new detectors will make it possible to give the edge to protons over X-rays. There are lots of advantages, or suspected advantages, to proton therapy. It would mean shorter and more effective courses of treatment, generally resulting in more comfort and a better outcome for the majority of patients. It will enable us, longer term, to tackle some major cancers that are not possible to tackle effectively at the moment."
Multi-disciplinary and international collaboration are key to the success of the Pravda project. A team of specialists from institutions including the Universities of Birmingham, Liverpool and Surrey, the Birmingham NHS Foundation Trust, the Coventry and Warwickshire NHS Trust, and the iThemba Laboratories in South Africa have been assembled to help tackle the many aspects involved. Their breadth of knowledge and expertise is vital, as Professor Allinson pointed out.
"As an electronics engineer, I build detectors, but of course I need clinicians, radiotherapists and medical physicists on board. You have to work closely with healthcare professionals and practitioners because they know what they want; I, as an engineer, cannot assume what they want."
Some of the detectors coming from the University of Liverpool are very high-speed detectors which are very similar to those used to provide evidence for the existence of the Higgs boson at the Large Hadron Collider in Geneva.
I concluded by asking Professor Allinson about the next steps for the continuation of the project now that the grant from the Wellcome Trust has been made available.
"We have to test the instruments at a real facility. There are 30 operational sites in the United States, and two or three will be built here in the United Kingdom. We have good relations with iThemba in Cape Town and we’ll be going there with all our instruments to experiment on ‘phantoms’, artificial structures which replicate human body parts or tissues, and on animal carcasses.
"We’re building a prototype, which is expensive, but it’s more expensive to build commercial systems. Many medical trials and safety checks will need to take place, and many authorities will have to give approval. This investment can only realistically be funded by commercial players. Hopefully they will take up that technology and translate it into a commercial product, to the benefit of patients."