> 
> I'm going to see the dentist today.
> 
> 
> 

If the dentist is female, should I say

> 
> (a) Ich gehe heute zur Zahnärztin.
> 
> 
> 

or

> 
> (b) Ich gehe heute zum Zahnarzt.
> 
> 
> 

I think (a) should be the correct version, but I'm not sure whether it's idiomatic. (Perhaps "zum Zahnarzt" is a fixed phrase.)