I call my T by his first name and he calls me by mine. I am his client rather than his patient. I think of "patients" as being more apt to call their T's "doctor." (My T does not have his PhD, so I couldn't call him doctor anyway, it would have to be "Mister" and that would be weird! If he asked me to call him Mister I might ask him to call me Doctor since I do have a PhD. That will never happen, of course, but it's kind of amusing imagining it.)