As I said, you don't know enough about what you are talking about. You won' t be worried until you get a radon-induced lung cancer, which isn't all tha t likely to happen, but more likely than if you lived in a safer area.
The advantage of getting worried before you get the lung cancer is that it can induce you to change your life - by perhaps putting an exhaust fan into your basement - in a way that reduces your chance of getting lung-cancer ( not to mention those people with whom you share the house).