So, good news, nine years of undetectable PSA after surgery may bode well for you. The generally accepted definition of a BCR is two PSA tests that are detectable, for a standard PSA tests that only measures to one decimal, that would be .2, then another test that comes in at .3. There is a lot of debate in the medical community about what constitutes BCR when using an ultrasensitive PSA test that measures to two decimal places.

Does your PSA test say <.1, before my urologist switched me to the USPSA, my PSA tests would read <.1 which didn't mean it was "undetectable" but that the sensitivity of the test would not measure below that.

When my urologist switched me to USPSA, I have readings like .07, 09, .126...

You say three tests over three months and it remains at .1. So, that would indicate no BCR at this point. Another useful clinical data point would be PSA doubling and velocity times, that would require your PSA to rise over multiple tests, something you are not experiencing.

So, you may want to consider actively monitoring your PSA, monthly may be "too much." You may want to consider every three months. Have decision points, are you going to use the standard PS tests or USPSA, frequency, if you do experience a continuous rise (determine what "contiguous" is, two tests, three tests, four...that would give you PSADT and PSAV. Decide at what point you would image, the recently approved PSMA imaging can detect below .5 but start to have high detection sensitivity at .5.

A reason for multiple tests is sometimes PSA will go down after rising, mine has done that twice, both times we did not hit the panic button as my medical team and I want solid clinical data before considering treatment.

Informed by clinical data, you can then make a decision about treatment, if and with what.

Here's a link to a short video on one of the newly approved imaging capabilities by the FDA - https://www.urotoday.com/transformative-evidence/clinical-application-and-utility-of-pylarify/videos/mediaitem/2129-the-diagnostic-performance-of-psma-pet-ct-with-18f-dcfpyl-in-prostate-cancer-patients-osprey-christopher-wallis-zachary-klaassen.html