Proton Therapy

04 October 2009

Interview with

Professor Karen Kirkby, University of Surrey

Chris -   Professor Karen Kirkby is at the University of Surrey and she's developing a way of treating cancer, using proton therapy.  Now, this is a targeted beam of protons, they're positive charges, and you can aim these at individual cancer cells to get rid of them.  Hello, Karen.

Karen -   Hello.

Chris -   Great to have with us on The Naked Scientists.  So, tell us a bit first of all about the problem with cancer that you're trying to tackle.  I mean, everyone's heard of cancer but it's a generic term, what do we actually mean by it?

Karen -   I think cancer covers a whole range of diseases and Kat covered it quite nicely earlier on when she said about the brain cells.  Obviously, we all like more brain cells, but we don't want them to go mad and form brain tumours.  And that's effectively what cancer is.  It's where the cells go mad and starts to form tumours in parts of the body where you don't want them.

Chris -   And so, if you could just summarize, what are the current strategies that we use to get rid of cancer, before we start talking about your technique.

MRI machineKaren -   Okay.  Well the current strategies, there's surgery which is very effective and you're looking at about 50% of cancer cures using surgery.  Then we've got radiotherapy which comes in at about 40% and then chemotherapy, which combined with the other two modalities comes in at about 11%.

Chris -   And your technique?

Karen -   Our technique is one that's used rarely in the UK.  There is a centre in Clatterbridge which uses it to treat eye cancers, but it's becoming very, very widely used in the states and Europe, largely because of advances in medical imaging.  You've got to see the tumour before you can use this technique.  So, it was thought about in the late '40s, but because at that time you couldn't really see the tumour, it wasn't very good to use.  It's a very targeted technique - whereas with x-rays, if you irradiate a tumour with radiotherapy, the damage that's induced by the x-rays is induced around the tumours, so in front of and behind it.   Whereas if you use protons and heavier ions, you use something called the Bragg peak - this is the way the ions actually stop.  And if you change the energy so that most of the energy is deposited in the tumour and very little in the surrounding tissue, then you can imagine you put most of the damage into the tumour, very little into the tissue in front of it, and practically none into the tissue behind it.

Chris -   So this is a way basically of minimizing side effects because radiotherapy is very effective - you're basically giving a beam of radio waves, x-rays, microwaves, whatever people are using, ionizing radiation into the cells.  This damages the DNA of the cells and they die, but the problem is, that as you say, it's unfocused and takes down adjacent tissues which are healthier and this make side effects.  How do you manage to target your therapy so appropriately just into the tumour itself then?

Bragg Curve for Alphas in AirKaren -   Well I think it's largely the physics.  Physics works as for us beautifully because of this Bragg peak.  You get a very, very sharp peak.  So, if you can imagine going in through the tissue, you put a tiny bit of damage into the tissue in front of the tumour then there's this big peak as the protons deposit their energy, and then beyond the tumour, there's practically none.

Chris -   First of all, can you just explain the proton bit of it.  Why is that novel and how does that work?  And where do you get these protons from?

Karen -   Well, protons as I say, they've been thought of for cancer treatments since the work was done or back in the - I think they've first proposed in 1946 and some work was done in Berkley in the states.  But the results were a bit unequivocal largely because they would irradiate a large amount of the body simply because they didn't know exactly where the tumour was because they haven't got the imaging techniques.  So, the results weren't particularly good.  But now, we can find the tumours, we can target the protons at them.  If we use MRI imaging for example, we can target the protons exactly at the tumour and it's very useful if you've got a tumour very close to a particular structure such as the spine because there's not an exit dose.  And therefore, you can put all the damage into the tumour and run into the vulnerable tissue beyond it.

Chris -   When the tumour gets impacted by the beam of protons, what do the protons do to the tumour.  Why do they destroy it?

Karen -   Well protons work in a very similar ways to x-rays, but of course, protons being bigger, they're particles coming in, rather than electromagnetic radiation.  They basically induce double-strand breaks in the DNA.  Now we know those double-strand breaks can be repaired, but they're much more difficult to repair.  And therefore, you can start to destroy the tumour much more easily than you could with x-rays.  It's sort of - it's a bit like throwing cannon balls, rather than ping-pong balls at the tumour.

Chris -   Which is a good thing.  The question is though, that as you've said yourself, now we have the ability to image tumours really well and we can see where they are and you can target your therapy.  That's fine.  But what's the resolution of the scanning?  In other words, one of the reasons people die with malignancies is not because of the primary tumour usually.  It's because it's spread to elsewhere in the body.  So, are you able to use this kind of therapy to pluck off, not just the primary tumour, but those spreads, those metastases as well?

Radiation therapy of the pelvis. Lasers and a mould under the legs are used to determine exact position.Karen -   It's being done a lot in Japan.  There are stories there in the literature of it being treated for small lung tumours and tumours in the liver, and it's been termed, the form of Atomic scalpels.  In Japan, they're tending to use protons and carbon ions.  So the Japanese are further ahead then we would be in the UK at the moment.  But they're using combined modalities of treatment and there are stories of fishermen being taken off fishing boats, taken to hospital, given something like 10 to 15 fractions, being flown back to the fishing boat and being completely cured.  As I said, these are some of the stories in the literature  and I've seen pictures of liver tumours where the tumour has completely been removed.  And for example also, tumours in kidney which would be difficult to treat with conventional radio therapy, simply because of the collateral damage on things like the bowel.

Chris -   And is it pretty much any kind of tumour or the specific kinds of tumour for which this is more appropriate?

Karen -   In the UK, the feeling is, first of all, it's for paediatric tumours because of - for example, if you're treating tumours of the spine in children, if you use conventional radiotherapy, obviously, you'll bathe the rest of the body in radiation.  You bathe things like the lungs and the heart.  And obviously in children, you want to minimize the chance of secondary cancers later on in life.  So that is one of the particular ones.  It's also very useful if you're close to critical structures.  It's part of the armoury.  It's not going to replace conventional radiotherapy, but it might be useful for cancers that we can't use radiotherapy for at the moment.

Chris -   Thank you , Karen.  We'll leave it there, but do stay with us.  That's Professor Karen Kirkby.  She's from the University of Surrey and she's working on charged particle beams for cancer treatment.  They use protons.  So needless to say, she's very positive about her research.

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