I fly probably once every month or two.
Every time I've told the dude who checks ID (before the screeners) that I've had skin cancer and cannot go through the backscatter, he (or she) has directed me to the line with only a metal detector. I've never been asked to show my surgery scars or any other "proof." (though I'm ready to whip off my shirt if anyone wants to see them) I've offered to go through the "medical needs" line, but I've never been directed there.
I've only been patted-down once.
The pat-down itself was not that bad. Roxy, I've got issues, too. Therapy helped me a lot for things like pat-downs and medical exams. Consider asking your doctor for a prescription for a couple valium pills. I've used them before the kind of things that do set me off, and they work great. Just enough to take the edge off but no sense of inebriation or being spacey. I couldn't tell I'd taken anything, other than the fact that I didn't have a panicked freak-out like I'd expected. People with me can't tell I've taken anything, either.
I like valium. You can get a prescription for only 1 or 2 pills. You don't even have to take them. Just knowing you have them if you need them is a huge relief.
"If Americans want to live the American Dream, they should go to Denmark." - Richard Wilkinson