Delos IV was the inhabited fourth planet of the Delos system. Beverly Crusher interned under Dr. Dalen Quaice on this planet in 2352. (TNG: "Remember Me")
According to Startrek.com, there were two systems named Delos and this Delos IV was not the same planet as Brekka. 
According to the Star Trek: Star Charts ("United Federation of Planets I"), Delos IV was listed as a member planet of the Federation in 2378.
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