Proton Therapy – Cost and Benefit

[T]he current question on whether patients do benefit from it better than conventional, less-costly treatment.

‘Proton therapy’ was one answer to the “what good is it?” question of physics when I was working at TRIUMF, and explaining the benefit of basic research wasn’t an option.

Proton therapy is the use of protons to destroy tumors or cancerous cells in a way that is more targeted than other treatments like chemotherapy or EM radiation; I can’t really get into the medical subtleties (dammit, Jim, I’m a physicist, not a physician!). EM radiation will attenuate as it goes onto the body, so if the target is below the surface, you’ll get more energy deposited in the healthy tissue in front of the target. Charged particles lose energy, by ionizing atoms or molecules, in proportion to their speed — faster moving particles don’t spend much time interacting with a given atom — and so as they slow, they are able to deposit more energy. This compounding effect means they deposit a large fraction of their energy in a small region, and the penetration depth where this occurs can be tuned, as it’s proportional to the incident kinetic energy.

So you do far less damage to the surrounding healthy tissue. The question, in Zapperz’s link, is whether that translates into an overall better response of the patients, and a cost/benefit analysis.

Here is a somewhat more detailed explanation of the physics, including a dose vs depth graph for EM, protons and protons with a modulated energy source to spread out the Bragg peak. Protons have an advantage over electrons for this type of treatment: because they are much more massive, they have a much greater tendency to forward-scatter and reach the target.