I don't know if you're doing it already, but in the interest targeting you can include professions too and it will target people who have it set to their "work" on FB; plus adding hospitals to workplace targeting you can quickly close the gap

And as another handy tool, you can use the FB ads api without authentication to perform certain types of search: http://graph.facebook.com/search?type=adworkplace&q=hospital... and build your targeting criteria

Hope it helps :)