This is my understanding of how radiation and ADT kills/or suppresses cancer cells -- someone please correct me if I am wrong:
Radiation. Radiation kills cells while they are in the process of dividing. It catches them at their most vulnerable -- with their pants down so to speak. Cancer cells divide a lot more frequently than normal cells, so a course of radiation treatment will proportionately kill a lot more cancer cells than normal cells -- and hopefully all of the cancer cells at the site being radiated. It won't kill cancer cells outside the site being radiated.
ADT (hormone). ADT treatment does not kill cancer cells, but it slows down the rate at which prostate cells divide. Both cancerous and non-cancerous are affected simply because cells continue to die off naturally, but are not replaced to nearly the usual extent. For this reason, ADT can reduce the size of both the prostate and any tumors, but will not reduce either to zero.
A low and not-rising PSA indicates at worst, inactive cancer cells, and maybe none at all. Radiation will have no effect on non-existent cancer cells (obviously!) and it will affect inactive cancer cells only to the same extent as normal cells. ADT will cause some cancer cells to die off without being replaced, but not all of them.
So my conclusion is that for inactive cancer cells, radiation and/or ADT will not do any good. Because of the side effects of those treatments, we are better waiting until clear evidence of active cancer cells -- rising PSA. And if there are indeed no cancer cells, or they remain inactive, we will never get that rising PSA, and will have avoided useless and harmful treatment.
Just my opinion of course.
Age 63. Other than cancer, in good health; BMI 20
Pre-op: No symptoms; PSA 5.7; Gleason 4+5=9; cancer in 4 of 12 cores
7 March 2008, RRP, non nerve sparing
Two nights in hospital; catheter and staples out after 7 days
Continent, no pads needed from the get-go
Post Op: Stage pT2 M- N-; clear margins and lymph nodes; Gleason 4+4=8; prostate weight: 37gm
6-week PSA: 0