radon radiation is primarily alpha. That is never good in any dose.

>In this multicenter trial, researchers enrolled 114 patients with moderate-to-mild knee osteoarthritis across three academic centers in Korea. Participants were randomly assigned to receive one of two radiation regimens — a very low dose (0.3 Gy) or a low dose (3 Gy)

This is gamma. Those doses are "low" because delivery here is localized. If given full-body the 3Gy has something like 25-50% mortality.

The cancer patient are delivered like 20-80Gy into the tumor and surrounding tissues which just kills cells outright.

The point is that "radiation" is multiparametric.