you can let them get off the bike before x-raying them...

I don't think pro cyclists are particularly health conscious. They're performance conscious, which is a very different thing.

The government already uses large X-ray scanners to X-ray vehicles with riders in them. The scanner manufacturers insist these X-rays are perfectly safe to use on humans even though they're strong enough to penetrate steel.

Millimeter waves won't penetrate metal, so they probably wouldn't work on bikes.

They'll dismount and give the bike to the x-ray tech, of course. Besides they got a bigger dose in the scanner at the airport.