According to PWInsider:
Say goodbye to the six-sided ring. TNA has a traditional four-sided ring set up in the Impact Zone for tonight’s Genesis PPV.
TNA had been using the six-sided ring since debuting at Universal Studios in May 2004 for their first Impact taping.
Good riddance to bad rubbish, even though the six sided ring did seem to have an invisible touch-ay… it reaches in and grabs right hold of my heart… – Dusty