Page 44 of Invasion of the Prostate Snatchers describes this:
"There is another unfortunate and little publicized side effect of radical
prostatectomy: interruption of the nerves that control rectal function. This
condition can lead to irreversible loss of sphincter control, with unpleas-
ant consequences such as fecal incontinence, otherwise known as 'wet
farts.'"
I experienced a little bit of this when going through IMRT and afterwards.
The doc said to take Imodium. It does help in my case. So far whenever I
have played farting roulette I have always won.