RXReplace: Invalid escape sequence: "\B".

I'm trying to add a calculated column to create abbreviations for a string using a regular expression in the RXReplace function: RXReplace([Hospital_Name],"\B[a-zA-Z'-]+","","g"). However, I get an error stating "Invalid escape sequence: "\B"." which seems to not recognize the not word boundary. The function does recognize the word boundary "\b". Why is this not working? Is there an alternative to "\B" or a different approach to abbreviate a phrase (e.g., "This Is A Phrase" > "TIAP")?

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