Impotence is a common effect of many prostate cancer treatments. Sometimes it is caused by physical issues, such as nerve damage during RP or the effects of castration. But prostate cancer also causes severe psychological stress, which can also cause impotence.
A cautious doctor might order an expensive and invasive test that uses an instrument to record penis girth throughout the night. Physically healthy men get nocturnal erections. The blood flow provides oxygen and nutrition to the organ.
Now researchers have demonstrated a much simpler way to find out if the problem is physical or psychological. They wrap the penis in a circle of postage stamps before bedtime. Upon wakening, if the circle is broken, there was at least one nocturnal erection.
Here's the PubMed link:
ncbi.nlm.nih.gov/pubmed/335...
and the description regarding the award of an IgNobel prize for this work:
arstechnica.com/science/201...