A little more context would help. Without the context, here is one guess (note that I am suggesting some of the changes so that your e-mail is not accidentally misconstrued to be argumentative).
"I apologize for that. Shall I use MRF as the subject or a more specific word?
Thanks in advance and best regards."
If you want a slightly more informal tone, you could change the first sentence to "Sorry about that." It depends a bit on the relationship that you have with your boss and the type of language you tend to use with each other.
If your boss is a native U.S. speaker, I would change Shall to Should.
Interested in Language