Sunday, June 29, 2008

Radiotherapy and Monte Carlo simulation

Britain's lack of investment in particle physics may ultimately entail that the chances of surviving cancer under the National Health Service are significantly less than in Europe or the US.

Conventional radiotherapy attempts to kill cancerous tumours with a dose of X-rays. Unfortunately, a significant dose is also delivered to surrounding tissues and organs. In contrast, particles with a non-zero mass, such as protons and heavy ions, deliver a dose of radiation according to something called a Bragg peak. As a consequence, proton therapy and heavy ion radiotherapy offer a more precise tool for the treatment of cancer.

The link with particle physics is that proton and heavy-ion therapy requires particle accelerators, such as the synchrocyclotrons used in pure physics research. And, whilst Europe, the US, and Japan are forging ahead in this medical technology, here in the UK we have next to nothing. In fact, at the M.D. Anderson Cancer Centre in Texas, children suffering from a particular type of cancer are each given: (i) an individual CAT scan, to precisely identify the tumour location, shape and size; (ii) an individual MCNP (Monte-Carlo N-Particle) simulation, to ascertain the required proton dose distribution.

In this context, it is worth noting that in the US, 66.3 per cent of men and 62.9 per cent of women have a five-year cancer survival rate, whilst in Europe the survival rate is 47.3 per cent for men and 55.8 per cent for women (Eurocare statistics).

As a technical aside, MCNP is an interesting type of simulation because it represents particle interactions as a type of probabilistic billiards. Rather than evolving a quantum mechanical wave-function, particles are given determinate particle tracks between collisions, but the interactions are probabilistic. The distance between collisions is probabilistically selected, the nature of the interaction is probabilistically selected, and the outcome of a collision, (the direction and energy of an outgoing particle, for example) is selected according to the quantum mechanical cross-sections. (In quantum theory, the probability of an interaction is specified by something called a cross-section; the greater the cross-section, the greater the probability).

For an introduction to these issues, my own paper on the subject, Dosimetry, Scattering theory, and Monte Carlo simulation, might be of some assistance.


Bob said...

I find it interesting that you see the UK as a competitor of the USA and Europe. Doesn't England belong to Europe? Probably not according to many of the inhabitants.
Certainly a German would never question if his medical standards measure up to the european ones.


(Dutchman in Germany)

Gordon McCabe said...

In this context, not a competitor, Bob, but a standard for comparison.

And the crucial point is that Europe doesn't (yet?) have a shared pool of medical resources; if you get cancer in the UK, under most circumstances you would, without significant additional expenditure, be constrained to obtaining treatment in the UK, under the nationalised health service.