This should be a reminder that we have no evidence that the Linear no threshold model of radiation exposure is accurate. In fact, we have compelling evidence against it. But due to rather aggressive lobbying effort by anti-nuclear activists, we are stuck with this idea for the time being.
It's simply the default that was decided on as the most conservative option possible, but that's pretty much it.
Radioactive baths have a rather long pedigree. In Jachymov, Czech Republic, they are used for over century. Sometimes they are even covered by health insurance.
https://en.wikipedia.org/wiki/Linear_no-threshold_model https://cs.wikipedia.org/wiki/L%C3%A9%C4%8Debn%C3%A9_l%C3%A1...
Some anti-nuclear activists are against LNT because they think it understates the effect of low dose radiation.
The conservative approach would be to assume low dose radiation has the maximum effect not ruled out by evidence. This would be higher than predicted by LNT.
Exactly, it could be that a few pretty high exposures are actually less damaging than frequent low but clinically significant exposures.
I think the point of the article is that there hasn’t been a lot of evidence for low dose radiation as a treatment.