BCR normally occurs when PSA after surgery hits .2 on a standard PSA test with a subsequent reading of .3, usually 90 days later.

The lower the PSA, the greater the chance of the elusive cure...but, that's based on the old notion that recurrence started in the prostate bed then progressed linearly to the PLNs.

That may be the case and SRT to the prostate bed is where the recurrence is and one is cured. Emphasis on may.

The more likely scenario is there are micro metastatic sites outside the prostate bed and SRT to the prostate bed only is destined to fail.

My mantra, be aggressive and match the treatment to the most dangerous situation.

If one decides to do combination treatment and radiation to the prostate bed and PLNs along with short term ADT then waiting for the PSA to rise between .5-1 (or higher) to increase your probability of a scan locating sites of recurrence and inform the treatment plan may not pose any risk to the outcome.

If one is only treating the prostate bed then waiting for the PSA to rise to increase the chances of locating with imaging doesn't pass my common sense test.

See if I can sum this up, if one believes that the more likely scenario is an increase in one's PSA after surgery indicates recurrence and you plan to treat with a combined regimen of short term ADT and radiation that includes the PLNs then it may make sense to treat once you have two or three PSA tests showing a continuous upward trend. The only thing in that case you may gain by waiting for PSA to increase to >.5 and improve your chances of the imaging locating the sites of recurrence is the radiologist can build a treatment plan that includes boosts and wider margins around the identified sites.

Generally, with confirmed recurrence, treating earlier, image only if it may change the treatment decision.