Yes, with advanced imaging such as PSMA (or even Carbon Acetate PET scans in the future) to identify a hot lymph node, or a hot seminal vesicle remnant, or similar, proton beam is probably ideal, and this may be standard in some years time. Also, it may be usable by those who've had max RT dose in some cases, although not in all cases.
Cupoftea,
I very much doubt BUPA would pay for proton therapy as a primary PCa treatment (and other insurers are even less likely to), so insurance probably wouldn't help you. You can't tell for sure if the cancer is confined until it's removed, and it's quite common for the staging to be upgraded during prostatectomy, and then radiotherapy needing to be done immediately afterwards. With Proton beam, you would be unaware of this until it starts spreading again, requiring salvage radiotherapy, which doesn't have as good outcomes as primary radical radiotherapy. With radical radiotherapy, the immediate surround is treated as well, together with lower doses to any spreading micro-mets, and it's more likely to mop up anything that a proton beam would have missed.
In the future better imaging and cheaper access proton beam could change things, but in the future, there will inevitably be more options. It's always better to get your prostate cancer in the future rather than now;-)