In 2036 I’d be 74
My first thought was, this is a clear trend of the PSA value, one could already radiate now.
However, after I calculated your PSA doubling time I recommend to wait. You have a doubling time of 33.7 months or 2.8 years. So you will reach the PSA value of 0.2 in August 2021. If you want to do a PSMA PET/CT you will have to wait until April 2025 when you reach 0.5.
So I do not know what the objective of this salvage radiation shall be. If you do nothing and just observe, you will have a PSA value of 8 ng/ml in 2036 when you are 94 years old. You will have no symptoms until then. And it is likely that you will die for other reasons until that time. In 2036 you could start with ADT, if required.
I calculated the PSADT from 5/18 - 0.09 to 7/19 - 0.12.