I would ask why not proton. Proton and IMRT seem to be equally effective, but proton has fewer side effects, and not just the transitory ones. Since it expends its energy in the tumor, rather than tearing its way out of your body, through your heart, for example, it's superior. I had one week of IMRT (photon X-ray) and 4.5 weeks of proton. There's no comparison in side effects...