Posted 8/17/2015 12:49 PM (GMT 0)
I think it is prudent to plan for adjuvant radiation now and keep open the option for a reprieve if your PSA goes undetectable at three months. They generally give a man at least that long to heal after surgery before they start the radiation anyway.
PSA has a half-life in the body, as I recall, of three to four days. If your PSA immediately after surgery was, say, 10 then, based on the half-life, after 3 1/2 days you would expect it to be 5. After a week, 2.5. After two weeks, 0.625. Three weeks 0.156. Four, 0.039. Five, 0.00977. Six, 0.00244. And, after seven weeks 0.00061, which I think most machines would read as "undetectable".
But, of course, nothing is ever that simple. As ChrisR mentioned, sometimes prostate tissue is, technically, "left behind" in surgery with positive margins but is cut off from its blood supply and quickly dies. While this is going on the dying tissue can generate a bit of new PSA in the blood and screw up the math I showed above. So, yes, seven weeks is a bit early to make a set-in-stone decision.
But, on the third hand, 0.275 is really high at seven weeks. I'd go ahead and plan for the radiation and see what your PSA does while you wait for it to start.