The backscatter x-ray body scanners are the only scanners to be concerned with, that and improperly shielded luggage x-ray scanners you stand next to, which run at a much higher power level. The newer luggage scanners that do a CT scan are still using x-ray, it just spins around the luggage.
mmWave scanners use non-ionizing radio waves, in the same spectrum area as mmWave 5G, in fact, but at a much lower power level. Radio waves have over a century of evidence and science showing that non-ionizing radiation can't mutate cells, which is necessary to cause cancer.
Ionizing radiation like x-rays, can. Likewise, flying in an airplane at an altitude above the protection of our atmosphere, and being exposed to the sun, also exposes one to ionizing radiation at much higher power levels. That being said, why would anyone trust humans in a mediocre security organization to properly maintain their machines? Especially now with the current admin gutting everything to the bone.