JoJoLA,
Dr King's high-risk protocol is experimental, and I can certainly understand why that might make you uneasy. But his goal is 85% biochemical control (the same as carbon ion) for high risk. If you are concerned about
not enough "overspray" from SBRT, you should have even more concern over carbon-ion, which has essentially none. Dr. King does IMRT on the same machine that he uses for SBRT - TrueBeam with RapidArc - and he sets the high-risk treatment margin at 5 mm with both. The big difference is 40 treatments vs 5, but also intra-fractional motion tracking (with SBRT) vs only inter-fractional motion tracking (with IMRT). The greater use of motion tracking avoids radiation "misses" that hit the bladder and rectum and cause toxicity - most would view that as a benefit, but I can see that you seem to view the lack of dose to those "organs at risk" as a problem. I can understand that if you, for some reason, believe the cancer has already spread to those organs, you would want to treat them, whatever the toxicity. But, if it were me, I would want evidence of that (Stage T4) first from an MRI.
Here's an article that discusses SBRT monotherapy for high risk patients:
SBRT for high-risk prostate cancerIf you don't want an experimental protocol, the standard-of-care that has reported the best biochemical control is a combination of brachytherapy and IMRT. This puts a much larger dose inside the prostate capsule where it is most needed, and a lower dose to surrounding tissues so that it does less damage. This is the kind of therapy that Michael_T and JNF had. You can get this at UCLA as well. Dr Kamrava will be taking over for Dr Demanes, who is retiring soon. Demanes reports 86% biochemical failure-free survival for high risk patients treated with this combo therapy.
There is also the possibility of using HDR brachy as a monotherapy (without IMRT) because HDR (unlike LDR) can treat an area outside of the prostate. This is experimental and there is a clinical trial at Stanford to explore this new use. You can read about
it here (this article also discusses the combination therapies):
HDRBT monotherapy in treatment of high-risk prostate cancerOne nice thing is that you don't have to go to Japan or Germany to get these therapies.