Usually the effects of hormone therapy dominate, and that continues pulling PSA down just as it does before RT.
If you have RT without hormone therapy, you'll see the radiotherapy will most likely at least half PSA (usually better than that), and then it will continue dropping to a minimum somewhere between 18 and 36 months after RT, before rising to new stable level. During this period you may get PSA bounces, where PSA climbs for 6 months or so (which can be very alarming) before falling back to a lower level than before it started climbing. PSA bounces tend to happen more in younger men with good immune systems. We don't know the precise mechanism, but it's likely to be related to the immune system mopping up dead cancer cells. If you are on HT, this is all masked by the HT.
PSA isn't usually measured until at least 12 weeks after RT, from which you might infer that PSA tests before this are not useful or clinically significant.
Edited by member 03 Jul 2022 at 16:20
| Reason: spelling