@karrows proton preferred in my case to minimize “collateral damage” to healthy tissue. As an example, my pelvic lymph nodes are positive and need radiated. With the bowel being in such close proximity, proton would presumably result in less damage to the bowel versus photon. While both options are effective when it comes to neutralizing cancer cells, proton therapy is more targeted and doesn’t pass all the way through the body like photon therapy. I initially had the same thought as you regarding a potential “benefit” with photon therapy to catch any nearby “floaters,” but was told the amount of radiation that hits surrounding tissue is enough to damage the healthy tissue, but not enough to “kill” any floaters. Thus, no real benefit; only more collateral damage. That being said, photon has come a long way and the odds for long-term damage are much better than several years ago. I hope PET scan brings good news for you.