As a survivor and a physicist in RadOnc (Score 1)

I hope your wife is doing as well as I am. Cancer is truly a bitch.

Protons are an attractive modality of treatment. They offer attractive depth-dose characteristics (see the previous mention of the Bragg Peak), a higher relative biological effectiveness (they kill more cells per unit dose), and do somewhat better on hypoxic tumors (tumors with areas of low oxygen concentration). And I admit, it sure would be a cool toy to have here at work. But...

There are many practical problems with proton accelerators. First is that they are HUGE; the bending magnet is often 10 to 100 times as large as that of an electron accelerator (used to make x-rays). There are not that many hospitals who have the real estate to accommodate such a machine. Because they are so expensive and expansive, most facilities will only be able to afford one such machine. What do you do when it breaks down? Radiation therapy outcomes can be quite sensitive to skipped days and breaks in the scheduled treatment course, which often are every weekday for 6-8 weeks (which is why we are treating patients on both Saturday and Sunday last weekend and this one, to give our patients Christmas and New Year's Day off without compromising their treatment). As for being "crisper and cleaner around the edges," advanced techniques in photon therapy do this pretty darn well. Intensity Modulated Radiation Therapy can construct dose distributions with very sharp gradients that are comparable to the distributions achieved by protons.

In the end, until superconducting bending magnets become cheap, or until plasma wakefield proton beams achieve the luminosity necessary to be useful in the clinic, protons will remain a niche market. And honestly, for most cases it would make very little difference to me if I or any of my family were treated with x-rays or protons.