This is the gamma sector, the Vendeen System is located in this sector.
Planets in this sector are able to maintain their independence because the area is far away from the Pangalactic Federation's center of government, no active anti-Federation power uses the area as a base of operations, and most of all, it is near the border of the Aldian Empire, the Pangalactic Federation's primary rival.
Lezonia is in this sector
A weapon based out of this sector of the Milky Way was what caused the Calnus (possibly after S04 because of the time frame), to be displaced in a warp, placing them near Roak, which is in the Theta Sector. The planet that was dystroyed in question was never mentioned.