I am glad you mentioned the Therac-25, that saves me the trouble of looking up the reference in reply to dwm650. And it's not the only such story.

Sure, the backscatter boxes are probably safe... but it sure would be nice if that could be better illustrated. Mistakes happen. Negligence happens. Machines break. Let's not just hope for the best. Let's not just trust.

They put more warnings on a bottle of beer than the backscatter checkpoints. Accurate dosage information should be mandatory as should a transparent maintenance schedule. Exposure adds up. It matters.

The keep-out zone info is REALLY interesting.