[@User]

Hey bud, I'ma help you out. Doctor Specialist? I don't think that's a thing, and it sounds terrible. Obviously your guy is a doctor, but what kind? Says he worked in a medical center, so I suppose a heal people kinda doctor, right? Well, what did he specialise in? Doctor Specialist sounds totally vague. 

If in doubt, just go with Doctor - that'll cover a blanket of vital medical skills. Smart idea by the way, the group is definitely going to need someone with those kinds of skills.