You cannot make the claim that releasing toxins is okay because some toxic elements occur naturally.
( Also, if your basement has a radon problem, you can mitigate it by better ventilation. You cannot mitigate a contamination zone without decades-long cleanup.)
Personal responsibility only assumes informed consent. This is why cigarette packs have warnings on them. I would argue that w passenger does have a case against the airline for not informing them that they are being exposed to cancer causing radiation even when everything this perfectly normal. The classic argument "but what about plane crashes? They don't inform you about that" is different, because crashes are.by definition abnormal, tragic, and rare. Whereas absolutely everyone on board is getting a dose every time they fly. As for medical exposure, I will go out on a limb and say that's covered under medical consent forms, and/or a medical research board has determined that the benefits from the dose outweigh the cancer risk.
But that only covers airline passengers, not employees that are getting orders of magnitude more dose. That only strengthens the argument that the airline shares liability. Do you think coal miners should have no case for lung diseases because maybe they got it from cigarettes? Or inherited it? Their employment put them in the position where they got exposed. Therefore the employer is liable for their illness.