50 bananas is an interesting quantity in that it is conceivable you could eat that many in short order, but I'd be worried about someone who did (but not because of the radiation).
The physcists we have had come in to check x-ray gear can generally do a conversion to banana equivalent dose in their head when asked. Seem to check out as accurate too.
The CT scan is the interesting one. I've talked to some researchers about CT scans, and how they do increase cancer risks. It's not very much, but for serious long-term conditions you might get several CT scans per year and that could increase your cancer risk. When looking up studies the numbers are pretty low, usually under 10%, but it is an interesting risk to be weight against diagnosing and treating the underlying condition.