I've always wondered about this: is the machine physically incapable of blasting you with a stronger dose than it's supposed to, or is that software controlled? Because there is no way I'd believe the software on that thing doesn't have a bug.
They aren't releasing the data for when these machines are audited for safety/compliance. https://www.oig.dhs.gov/assets/Mgmt/2015/OIG_15-86_May15.pdf