[MengerSponge]

In the early 20th century America also used to have lots of radiation therapy providers. It's quackery, and harmful quackery at that.

Just because you have a tradition of something doesn't mean it's effective. Or safe. Or wise.

[kensai]

People with rheumatological diseases beg to differ. I understand nowadays it's a little bit odd, given the more sophisticated technological therapies that exist, but getting exposure to radon in certain calculated doses is how it was supposed to work.

I agree that the mechanism of "radiation hormesis" is kind of weak, but it has not been disproved as quackery either. https://en.wikipedia.org/wiki/Radiation_hormesis