I just finished IMRT on November 18 for a local recurrence (had a RARP in 2015). Going in, my PSA was basically 0.1. (usPSA from Labcorp = 0.094; regular PSA from Quest = 0.11). Won’t retest PSA until February 18 (3 months post RT). As has been stated already, a recovery period from the radiation is needed to get any meaningful numbers. I had a good discussion with my RO about the clinical significance of small variations in PSA tests and especially in ultra sensitive PSA tests. She made it clear that my PSA could bounce around for a good long while (as in many months), and that she would only be concerned when there was a consistent upward trend beyond 0.1.

I totally get your angst about PSA values post treatment (I’ve been doing this for ten plus years), but I’ve also come around to rounding off those last digits given that they can be simply due to lab variations (I’ve read that lab testing can vary by ~20% at low PSA numbers). To me, 0.19 and 0.23 are within limits of lab variance.

I found these short articles helpful:
https://www.pcf.org/patient-support/diagnosis/monitoring-detecting-recurrence/part-four-psa-after-radiation-therapy/
https://biologyinsights.com/is-0-04-psa-considered-undetectable/
https://scienceinsights.org/what-is-considered-an-undetectable-psa-level/