A recent study finds no support for a widespread belief that low-dose radiation from X rays and CT scans causes cancer. The notion that X rays cause cancer is based on a linear no-threshold (LNT) model used to estimate cancer risk from low-dose radiation. But according to the study authors that model is unproven and outdated. http://www.arbiternews.com/2016/02/05/no-proof-radiation-from-x-rays-causes-cancer-study/
Not a very useful study. I. e. absence of proof of damage is not proof there is no damage; however for even more damaging cosmic rays, that was proven in 20 year study ending back in 1970 comparying cancer rates in Denver + Salt Lake City with low altitude cities. - no difference found. See: http://www.jstor.org/stable/3573965?seq=1#page_scan_tab_contents
The paper you quote is interesting. Presumably, taking the two together, one has a fairly compelling story. The authors of Plasma's paper point out that the historical treatment of medical radiation assumes no "safe" threshold, below which the body can tolerate damage without ill effect, while the paper you quote provides evidence that there must be such a threshold, since if there were not then there would be a correlation with exposure to cosmic rays due to altitude. Ergo, the approach to medical radiation is unnecessarily cautious.
