Proposed Canon
First Mention: LIAB Epilogue 11
Some Healomancers gain the title of Doctor. Pierce used this fact to encourage a captured Lilith not to be shy about needing to use the latrine in front of him. Presumably because he's "seen it all" and will treat her professionally rather than oggling her.
Doctors are Master-class Healomancers.
There is a "bar" or other peer association of Healomancers that reviews who can gain the title. Alternately, being a doctor is unrelated to level, it is earned some other way, such as battlefield experience or training in Erfworlder anatomy.