Whenever we approach someone of a higher rank it is appropriate, compassionate, to provide the proper salutation. In the case of us RTs and RNs, we refer to doctors as doctors. That's doctor Smith to you.
I write this because I have a couple friends of mine, people who used to be fellow RTs and RNs, who are now doctors. At first I wondered how I should greet them. Then I decided that they worked hard to earn the title of doctor, and they should get due respect.
Just by calling a doctor a doctor does not mean they are above you in any regard. They are fellow men, they are unprofitable servants of God just as you and I are, seeking to make the world a better place by the time they leave this world.
I have only one time in my career as an RT, in my 15 years working with doctors, had a doctor tell me to call him by his first name, and that was the only doctor I ever called by his first name. Other than that, the compassionate thing to do is for all of us to give due respect, and call Dr. Smith a doctor and not Sam.