Ask Hopkins about the margin advantage with photon. It depends upon the machinery. If the treatment margins are lower with photon, consider it because of the near the bladder G7. My understanding is that the side scatter with proton is greater than photon which makes it a better choice than proton for the prostate. Do you have a link for the the issue of bladder protection. Thanks. I appreciate your question. Have a similiar (though worse) situation. Have decided upon viewray MRIgRT because of the margin advantage.