Yes, radiation exposure is cumulative. As a technician I wear a dosimeter and get checked for exposure 3 times a year. My concern is that frequent flyers such as business people etc...may be getting too much exposure regulated or otherwise from these machines. I'm would think the machines had to meet FDA approval before being put into use, but that doesn't necessarily mean that the cumulative exposure couldn't cause issues down the line particularly for children.
Regarding the 4th Amendment...I'm not a lawyer, but in continuance with other arguments I've listened to the body scanners and these new "enhanced" pat downs as the TSA calls them certainly seem to skirt the boundaries of what is unreasonable if not exceeding them. There have been spurious legal challenges to the TSA's methods but what needs to happen is a concentrated suit that will make it to the Supreme Court because that is the only way this issue will be resolved unless of course Congress steps in and puts a leash on the TSA, and I'm not even sure they have that kind of authority.
"You'll find that many of the truths we cling to depend greatly on our own point of view."