It looks like the Memorial Sloan-Kettering Salvage Radiation Therapy nomogram on Nomograms.org (direct URL: http://www.mskcc.org/applications/nomograms/prostate/SalvageRadiationTherapy.aspx ) has been updated. It's now easier to use and the response makes sense. It used to give your result as post-surgery rather than post-radiation.
I had been thinking that the nomogram was too pessimistic, compared to the paper version. But what I didn't realize was that four months after the paper version was released in the Journal of Clinical Oncology, an erratum was published that corrected a mistake in regards to pre-radiation androgen deprivation (hormonal therapy). The corrected PAPER version of this important tool is here: http://jco.ascopubs.org/content/vol25/issue26/images/large/zlj0150759390003.jpeg ; however, I see no reason to use it because the digital nomogram is much easier, quicker to use, and less prone to human error.
Now both paper and online versions tell me that I've got a 39% chance of being progression free at 6 years. That jibes pretty well with Catalona's research that showed that long term success with prostate salvage radiation is uncommon--only about 25% of patients overall are progression free at 10 years. Of those who had a complete response to radiation, as I did, Catalona found that 35% were free from PSA progression.
The full text of the original article (remember, the nomogram in this original article is not correct) is here: http://jco.ascopubs.org/cgi/content/full/25/15/2035.
If you have a rising PSA after prostatectomy, and you're considering salvage radiation, I encourage you to read the original article and use the online nomogram at Memorial Sloan-Kettering.