Hi Dave, u' right, x-ray films can be used in large format. I was in a hospital in 2005 and the operator was a woman, photographer in her lost hours. She showed me how the film was exposed, the film is not much X-ray sensitive but is pressed to a phosphoric screen with intensification. This screen converts x-ray into blue or green light.
So: the X-ray film is light sensitive, 100 to 400 iso but orthochromatic. As i used the maco orthochromatic filsm, i appreciate the X-ray films, because of the Thick polyester, quantity of silver, cheap prices, and fast process of treatment in red light.
So u had a good idea....