Jannett--
I wish I had some knowledge about
such advanced PCa so that I could offer more than my sympathy and strong wishes for some good news for your father and yourself. He's lucky to have you.
I found this article on Lutetium PSMA therapy for men with PCa. Probably you've seen it already, but in case not:
/www.ncbi.nlm.nih.gov/pmc/articles/PMC5355374/