Proton therapy definitely has some advantages over conventional XRT, and these are very helpful for certain types of tumors. However, even if it were proven to be beneficial for the majority of cancers, I don't think that it could find broad acceptance until smaller, more affordable delivery systems are designed. In the end, economics will win out over a couple of percentage points of improvement in local control rate or survival. Otherwise, proton therapy could remain restricted to a handful of large centers and serve as good advertisement for patient recruitment (MD Anderson will have to cut that video down if they want to run it during the Super Bowl...
)
Many people in radiation oncology think that the future of the field lies on the biology rather than on the physics side. There will definitely continue to be further, exciting technical innovations, but major advances in local control or survival rates will most likely come from molecular interventions that potentiate tumor killing or protect normal tissues. Check out the Presidential Address by Ted Lawrence at the most recent ASTRO meeting (
http://209.63.36.22/astro/Lawrence2/Lawrence_2.htm) or this recent review in Nat Rev Cancer (
http://www.ncbi.nlm.nih.gov/entrez/...ve&db=pubmed&dopt=Abstract&list_uids=15343280) for some thoughtful discussions of this topic.