Regular expressions Ignore case in search, but do not replace

In C #, I want to be able to replace text altogether, ignoring case in search, but not in replacement (kind?). Here's an example:

I have a list that looks like this:

Site → Location

Item → Items

etc...

Then I want to call ConvertMyString ("Site") and return "Location" to it.

While it works for me, BUT ...

If I call ConvertMyString ("site"), I would like it to return "place" (lowercase).

Is there an easy way to do this with RegEx or something without having to list all uppercase and lowercase versions?