They rely on the PSA to determine when to Image with PSMA PET. They told me they would wait until my PSA rose to 0.2 before they considered doing another PET From 0.2-0.5 PSA the PET is about 50-60% sensitive. Imaging below 0.2 likely won't show where the cancer is. There is a rare type of prostate cancer, neuroendocrine, that does not elevate the PSA so they do a bone scan and CT every year in the unlikely event that type of cancer is present.

Johns Hopkins (my MO) uses < 0.1 as undetectable. That is what Labcorp tests. They don't use the ultra sensitive PSA test. It is not as reliable at very small number and can fluctuate. Also, if you aren't going to Image or treat until it gets to 0.1, why do the test? I did get an ultra sensitive PSA performed at Emory (where I got my Radiation-they are close to where I live). It came back < 0.014 which is their undetectable number. It varies some by lab and institution.

My MO at JH is very experienced and is the Director of the Brady Urologic Cancer Research Center. He has written (or co-authored) around 500 articles) mostly on prostate cancer. With the rapidly changing treatment options, he believes in individualizing therapy. He believes in balancing quality of life. He has specific reasons for what he does and doesn't do. He doesn't follow a Standard of Care or protocol in the literature as it is changing so rapidly with new advances. Each person's case is different. Different age, Gleason score, stage of cancer, co morbidities, response to treatment etc. He did present me with the options of treatment. I asked "What do you recommend?". He told me and that is what I did.