Injecting anything experimental into the prostate is going to be impossibility in traditional medical arena.
Urologist have done other injections but if you can't find a urologist to inject a simple Antibiotic into prostate for chronic prostate infections how are you going to get him to inject anything else?
An oncologist? You might find some that will inject non-approved substances into prostate, they are protected by compassionate exemptions and have greater powers to experiment with individual cancer patients.
Mayo clinic, with other cancers, have taken this direct application of chemo/meds to tumor sites using surgical procedures and have much better success than systemic treatments.
Also, photodynamic therapy is being used by some cancer centers and I might be wrong but I think they do this on prostates.
The idea of sodium bicarb, in theory, is a step in the right direction. Raising intra cellular ph will decrease pain, slow the spread of cancer. However, typically sodium does not cross over cancer cell membranes because it is a weak electron attractor by virtue of its molecular weight, (according to some scientists,) so personally, I would seek out heavier metalic salts if alkaline therapy is your goal, (raising ph.)
By far the heaviest metalic salts are rhubidium and cesium chloride.