This has been known for decades. The more time at altitude the LESS you should be exposed to other forms of radiation. That's why they ask you questions about flying before any medical procedure involving radiation.
I'll bet the pilots are incredibly pissed about all these scans because for one thing it can reduce their legal flight time.
In the US, medical exposures are not counted against occupational exposure.
To make things worse these things are not just your normal transmission x-ray where you just want to see what photons make it to the sensor and the dark spots tell you where the dense stuff is. What these scanners are doing is providing far more radiation with the aim of getting atoms to absorb and re-emit photons - effectively making you radioactive while the scanner is on. The idea behind that is the wavelengths of the re-emitted photons can be used to determine what elements are present, find metal and perhaps find explosives. Because that really adds up to a shitload of radiation if it's going to scan all the way through you the dose is cut back and you just end up with the skin being exposed to quite a lot and no ability to sense internally hidden explosives.
No. The x-rays being detected are those that scatter off the person being scanned. They are *not* making anybody radioactive in any way. There is no way scattered x-rays are going to tell you the elemental composition of anything. Density, but not composition.
It is also not a "shitload of radiation". If these machines were detecting transmitted radiation instead, that would actually require *more* radiation exposure and would operate more like x-ray units found in hospitals.