Hospitals Look to a Nuclear Tool to Fight Cancer

The feed points us to a NYTimes article about hospitals using particle accelerators to treat cancer. While expensive, proponents say that the proton beams generated by the accelerators are more precise than conventional X-ray radiation therapy. This results in fewer side effects and reduced irradiation of surrounding tissue. The technology's critics say that the cost is not justified by a measurable increase in the level of care given to the patients. Nevertheless, this is an excellent example of "pure scientific research" leading to a useful, unrelated technique. From the NYTimes: "Tumors in or near the eye, for instance, can be eradicated by protons without destroying vision or irradiating the brain. Protons are also valuable for treating tumors in brains, necks and spines, and tumors in children, who are especially sensitive to the side effects of radiation."

Comments

Re:Side Effects?

[ZombieWomble]

Based on a couple of assumptions*, the entire reason for making use of this therapy is to mitigate the side effects of traditional radiotherapy. In traditional x-ray based therapies, the energy from the beam is deposited nearly continuously along the beam length, giving a roughly exponential falloff (I say nearly, as there is an initial buildup at the surface as secondary particle counts build up, and it is from the peak slightly below the surface that the exponential falloff begins).

By contrast, accelerated protons deposit their energy almost evenly, at a relatively low rate, until they are slowed to a certain energy, at which point their deceleration rapidly increases, accompanied by a massive increase in linear energy deposition. This leads to the "Bragg Peak", which offers a much, much more accurately targeted beam than is possible with conventional sources. (See this illustration as an example - compare the red line (in this case, C12 ions, but a similar principle) to the green line (an 18MeV photon beam). By carefully tuning the beam energy and orientation this point can be scanned over the tumour volume, giving a very localised dose deposition.

What puzzles me is why this is news - I was under the impression that this concept is well-established, and has been fairly well verified already. Just some fluff to fill up the science and medicine section, maybe? Now if it was about the CERN anti-proton tests, that's certainly something with a more dubious cost/benefit analysis...

* - I say a few assumptions, these are basically the principle ones behind all radiotherapy - that is, that all dose at the end of track structures is created equal and all dose is bad according to the LNT. While these ideas may not be strictly true, it is unlikely for them to be so wrong that it would invalidate the treatment as a whole.

Re:Side Effects?

[johnny maxwell]

Since they are accelerated, I'm guessing they penetrate further, but they will be stopped quicker too (charge, mass, volume, all these will make them easier to stop than high energy photon radiation). Best of all, it's the stopping/slowing of the protons that kills the cells (they hit stuff, break stuff, and stop/slow down), so less energy will be needed since the majority of the high-energy photons would just pass through. The trickiest part would be to determine how many protons and with how much energy.

For a nice picture of energy deposition vs. depth see e.g. http://www.gsi.de/forschung/bio/energy_e.html
One can adjust the peak energy deposition's depth by varying the proton's energy. The surrounding tissue gets a much lower dose than in X-Ray irradiations.
Combine the particle accelerator with a PET (http://en.wikipedia.org/wiki/Positron_emission_tomography) and you can irradiate a cancer with cubic millimeter resolution.

This is actually not a new, purely academic technique, it is already commercially available, see http://en.wikipedia.org/wiki/Proton_therapy

Attention: I'm not a doctor but a physics student :)