If someone in TV-land is referred to as "the doctor", it means he's a medical doctor. It might not be explicitly mentioned, possibly even outright denied, but anyone called the doctor seems to be able to deliver any and all surgical operations and medical Techno Babble required by the plot. There are no exceptions (well, other than him). All those other guys who've got doctorates in science, law and philosophy are helpfully distinguished from real doctors with vaguely-academic titles like "professor", if they're even awarded one at all.