I believe the 100 and 400 speed refers to system speed: The imaging system consisting of the film and the proper intensifying screens that fluoresce under x-rays to expose the film. Place the wrong kind of film into the wrong kind of screens and the resulting system speed drops to around 10 (as I guesstamate from my experience in x-ray). So green x-ray film isn't the same speed when exposed by light in a camera as TMAX 400, nor is blue x-ray film the same speed as Delta 100. I don't believe any ASA/ISO number has been assigned to x-ray film used in-camera and exposed to white light.
Ralph
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