doc in a box

[Herb Stahlke]

Does anyone know the provenance or history of the term "doc in a box" used to refer to immediate medical centers, those places where one can be seen by a doctor without an appointment and without going to an emergency room?

I've heard the term used in this way here in Central Indiana, but several web searchs bring up only internet medical sites as a referent for the term.

Thanks,

Herb Stahlke