Another interesting article:
Salvage Radiotherapy After Prostatectomy: Who Benefits?
Gerald Chodak, MD
February 07, 2018
Today's topic is multiparametric MRI and gallium-tagged prostate-specific membrane antigen (PSMA) PET scans for identifying disease in men with a low prostate-specific antigen (PSA) after radical prostatectomy.
If we are going to select men to receive salvage radiation, it is inherent that we select the right patients. We know that the disease can be either in the prostate bed, elsewhere in the body, or in a combination of the two. We have not had good ways to identify those patients.
There is a nomogram that has been used, the Stephenson nomogram, which has been updated, but its inaccuracy rate is about 30%. Now we have a study by Sharma and colleagues, who performed multiparametric MRI prior to radiation therapy in 473 men. It was not a controlled study but a retrospective analysis. They found that if the scan was positive in the prostate bed, then 88% of the men [with PSA ≤ 0.5 ng/mL] did not get a PSA recurrence with their  years of follow-up.
In contrast, if the men had a negative scan, then only 61% did not get a PSA recurrence. The use of the scan was at least able to identify men less likely to benefit. The problem is that the study was not prospective and there was no long-term follow-up, so we cannot evaluate whether salvage radiation had an impact on survival.
A second study, by Emmett and colleagues, looked at the PSMA gallium-tagged PET scan. It was able to identify disease both inside the prostate and outside the prostate bed. The findings depended, in part, on the PSA. If the PSA was < 0.2 ng/mL, 50% of the men had a positive scan. If it was > 0.4 ng/mL, about 80% had a positive scan. This could identify disease both inside and outside the prostate bed. Results depended, in part, on where disease was present. If disease was only in the prostate bed, then radiation had a better response rate compared with in men who received radiation when the disease was not in the prostate bed but elsewhere in the body.
The point of discussing these two studies is not that they prove or disprove the value of salvage radiation; rather, they offer an opportunity going forward to design a study that may help prove or disprove the value of this treatment. After all, if we know that disease can be detected, even at PSA levels as low as 0.1 ng/mL or 0.2 ng/mL, then it is critical that we use these tests in a future study to design the proper analysis and figure out whether salvage therapy works. We can make a case to use both of these scan methods when designing that future study, and hopefully such a study will be done. Ultimately, we can find out whether delayed radiation for a rising PSA will have an impact on survival.
1. Sharma V, Nehra A, Colicchia M, et al. Multiparametric magnetic resonance imaging is an independent predictor of salvage radiotherapy outcomes after radical prostatectomy. Eur Urol. 2017 Nov 28. [Epub ahead of print]
2. Emmett L, van Leeuwen PJ, Nandurkar R, et al. Treatment outcomes from 68Ga-PSMA PET/CT-informed salvage radiation treatment in men with rising PSA after radical prostatectomy: prognostic value of a negative PSMA PET. J Nucl Med. 2017;58:1972-1976. Abstract