Proton Therapy Congress 2016

Pursuing the 'elusive' proton CT 

Prof Nigel Allinson - University of Lincoln, Lincoln, UK

Could you tell us about the PRaVDA system?

One of the things you would like to do is to actually plan using proton imagery rather than X-ray imagery which is what we do now. This is really because protons and photons react differently, stop differently. But imaging with protons is difficult so we’ve built a machine, we’re not the first in the world but we’re the first to do it in an integrated fashion, to build it totally solid state. We record the trajectory of every proton coming into a patient and the trajectory of every proton coming out of the patient and what energy is left in the patient, left after the patient so we can work out what is deposited in the patient. From that we can develop the stopping power proton CT.

Are the machines quite large?

Yes, it weighs over a tonne. It will not be like that in practice and you can see, as shown in the odd slide of the Fermi Labs one, theirs is even worse looking than ours. Yes, it’s a prototype, it’s not a commercial machine; we’ll get it down much tighter. If some of the things I spoke about today, how we can do CT and not have this expensive range telescope, this thing that measures the residual energy of the protons that go through the patient, then it can make a very compact system and you build that into the couch and into the gantry or whatever the delivery system is. It would be more compact than a typical cone beam x-ray system.

How long do you see this process taking?

One or two groups around the world, including ourselves, have demonstrated that proton CT is possible, the quality is there, and it’s now engineering, if you like, a commercial prototype and then going on to trials and so on, getting it into application. I think three years.

What do you think is required to get us there?

Certainly what I think is required is much better instrumentation. We know what we’re doing, we understand now not just the advantages of proton therapy but also its limitations in how we can distribute dose. But we need to monitor that in real time – during treatment to replan at frequent intervals, to compensate for anatomical changes, patient movement everything else. Then, as I say, we can provide optimum treatments and not just what we have to do now is robust ones.

Some people say that imaging is the next step necessary for proton therapy. Your thoughts?

I’d like to think right, I think we’ve also shown that something which is technically difficult is possible, that we are beginning to show that there is a whole new field of charged particle imaging, not just protons but perhaps other charged particles as well, and there are a variety of ways we can get these images using the properties of the protons or the other charged particles and how we fuse that with conventional images. That’s a whole new field, yes, and an exciting one and one I think we can make a great deal of difference.

What are your thoughts on the conference?

There’s been a serious effort to bring together quite a representative group of leading experts in the world. So if you like I’m the one imaging expert here and that’s useful because I don’t really have to argue with any other imaging experts, that’s always an advantage. So it’s good to meet people from other groups and there are other aspects and there’s quite a few of the guys I know anyway so it’s good to catch up.

Any final thoughts?

We have some opportunities at the moment to potentially commercialise what we’re doing. We have to optimise many aspects of it. We have to take into account new delivery systems, pencil beam systems. In the longer term, if you like, on call it the software side, we have to see how we can make use of all these different proton CT images, how we can merge them together, how we can fuse them with other types of imagery like X-ray imagery. So it’s the beginning of a whole new field of, if you like, charged particle imagery. Then beyond that we’ll probably look at helium because helium has many advantages, potential advantages, for treatment and our prototype equipment could be used to image helium and we’ve got access to some helium beams. But I don’t think anyone is going to throw away their multi-million pound investment in protons for helium just yet.