I can't speak from my own experience for the post-radiation drop, because I'd been on ADT (Firmagon) and ARSI (Erleada) for six months by the time they radiated my prostate, and the meds had already reduced my PSA to undetectable levels.

For me, the radiation (both to the surgery site and months later, to the prostate) were just to give the cancer an extra kick while it was down. We don't fight fair with cancer any more. 🙂

Not many years ago, at stage 4b they would have given me only palliative treatment to manage pain. Now they recognise my cancer as "oligometastatic" (just one metastasis in my case, though it was a doozy) and — with my enthusiastic agreement — treat me with "curative intent," including high doses of radiation, even though it's most likely we'll just hold it at bay for years (or decades).