Carlos, you hit the nail on the head--what to do if your odds of success are low? Because the other way, your decision is almost made for you.
In my case, my odds of success in the short time frame provided by the nomogram are 38%. So far, it looks like I'm in the 38%. But you should be aware that Catalona and others have shown that at 10 years out from SRT, the overall odds of being progression free are 25%. The odds are better if you have a complete response (i.e. PSA falls below 0.1). Complete responders have a 35% chance of being progression free 10 years after SRT. So the odds are almost certainly against all of us SRT guys, given enough time. Of course, having PSA progression later on does not mean one will die from prostate cancer, but it is something I think about, especially given my age. If my PSA starts rising in the next few years, there's a better than even chance prostate cancer will be the end of me.
Another way to look at it is that the gamble is (generally--there are always exceptions) not a bad one. Usually the side effects from SRT are mild, especially compared to what men have already gone through from the surgery. That was my experience, and that of some others here, though not all. So that's the downside of the gamble--the risk it won't work and the person ends up with a lower quality of life. The upside is tremendous, however--a second chance at a cure. And even failing a cure, SRT can buy years of life free from the side effects of hormone therapy and chemo.
For Dr. Catalona's study, see the abstract here:
Dx Feb 2006, PSA 9 @age 43
RRP Apr 2006 - Gleason 3+4, T2c, NX MX, pos margins
PSA 5/06 <0.1, 8/06 0.2, 12/06 0.6, 1/07 0.7.
Salvage radiation (IMRT) Jan-Mar 2007
PSA 9/2007 and thereafter <0.1pcabefore50.blogspot.com