Well, my question is:

Let's say you go to Dr. Сергей Владимирович Живаго

How do I address him?
If I happen to be another doc working with him...I'd use вы + Сергей Владимирович, Сергей or Серёжа.

What if I were a new patient that is abs. strange to him and vice versa? Господин Живаго? (No "Доктор..." pls )