As for percentages of pedophiles suffering from tumors...it is probably very low. Once again, you're suggesting killing them all and not worrying about extenuating circumstances (brain trauma, mental retardation) or the possibility of their innocence.
Here's the one case study of a tumor I know of:
http://216.117.159.91/crimetimes/03a/w03ap5.htm
Note a quote from another web site:
Neurologist Daniel Tranel of the University of Iowa has seen people with brain tumors lie, damage property and, in extremely rare cases, commit murder: "The individual simply loses the ability to control impulses or anticipate the consequences of choices."
There is also a strong correlation between serial killers and head trauma. I posted elsewhere a case study of a young man who killed his mother and molested his corpse after having fractured his skull on a fall from a horse. The kid was normal prior to the accident, and went through an instand personality change.