Hey Ken, as you can see we're all pulling for you in whatever way we can. I'm lucky to have a friend who is really well versed in Medicare in all its forms. So I copied your initial post and sent it to him (anonymously of you of course). I'll paste his reply below and if the site permits it I'll include the two attached .pdf's he sent.
One thought that came to me as I read his note; he used the phrase "Extra prostatic extension". Sure, that's the same as what you said but just a word's worth of difference. You might try same meaning words that are slightly different since your appeals are going to mostly laymen, not real doctors (I suspect). Just my untrained thought.
Dave's response below:

There are some important questions that would help to clarify your friend's situation that I've listed below. However, although I'm certainly not a doctor, but it seems quite odd that a PET scan would be disallowed for Extra prostatic extension of the prostate.

General Information

Medicare Advantage (MA) plans can make medical necessity determinations, but the if an MA member disagrees with the determination they can appeal the decision that can eventually reach Medicare.

I'm attaching two excerpts of the Medicare website, which give you a more detailed description of the Medicare Appeals process. Ken, we'll do this on a one to one basis. I found a way to send you a private message 🙂

Please note that the second level of appeal is a review by an independent party and the fifth level of appeal is with a Federal judge.

Since the Federal website is interactive, below is the Medicare Appeal link so that you can further explore the issue.
https://www.medicare.gov/claims-appeals/how-do-i-file-an-appeal#:~:text=An%20appeal%20is%20the%20action%20you%20can
Questions

1) Is the MA plan denying any further diagnostic procedures?
2) Is the MA plan allowing some diagnostic procedure, but not the procedure that you want?
3) Have you already filed a Medicare appeal?
4) If so, what is the current status of the appeal?

Please let me know if you have any questions.

Ken, Keep punching with all you've got!
Good luck Buddy!!