As I understand it, when PCa is treated with radiation therapy, the theory is cancer cells are more vulnerable to radiation because they divide more rapidly than normal cells, and they do not repair damage from radiation, while normal cells can.
The situation seems to be complicated if the person has BPH, since that would also contribute to the total PSA.
So the PSA comes from Normal prostate cells + BPH prostate cells, + PCa cells.
If someone started with a low volume PCa, that was treated with radiation therapy, verses someone with a large volume PCa that was treated with radiation therapy, wouldn't that imply the NADIR for the small volume PCa would be higher than the NADIR for a large volume PCa, since the low volume PCa also would have more normal cells, that would be less damaged than the radiation?
The reason I ask this question is because I see various places indicate that after radiation therapy the PSA should be less than a certain amount, but wouldn't that PSA value depend if it was a large volume PCa verses a small volume PCa?
It is easy to understand if the entire prostate is removed, because in that cause there should be zero PSA, unless something was left behind.
Any thoughts how they determine what the NADIR should be after radiation therapy?
PSA and NLR after RP. What to make of these numbers?
Is radiation therapy warranted
PSA Too Low To Be Treated With Radiation?
Rising psa after Eligard and bicalutamide, in 9 months. What treatment now to stop the psa rise? 
Nadir is specific to each individual. Simply put lower is better though getting there longer seems to be better than quicker. With radiation progression is considered either 3 rises is PSA in a row, as it may bounce, or nadir + 2.0. Not sure about low volume or high volume as I have never seen that quantified on anything during my treatment. I guess more mets might be higher volume, or a larger PG but neither of those correlated to a volume in my treatment. Hope I answered your question or at least part of it.
Then it isn't necessarily a straight consistent downward slope, but ideally a downward trend.
It could be either. I read your profile, are they not concerned about your possible lymph node involvement?
No they’re not. They said the PSMA does not indicate lymph node involvement. It is equivocal. Both the radiologist and radiation oncologist indicated they see a lot of this in practice, and it isn’t uncommon.
I am waiting on decipher results, and will be consulting with a Prostate oncology specialist, and at least one other person on this to see if they concur. Needless to say I am still concerned, even though there was NOT enough increase in radiotracer uptake to suggest cancer, which is why I will be consulting with a couple of other physicians.
I read your bio also treedown. Do you mind sharing where you went for treatment?
Your results look terrific, and I wish you much continued success.
Take care,
John
At Treedown. Agreed !