An 18” panel can cut safely on a typical cabinet table saw. The trick is to turn the miter gauge so it runs backwards in the slot. You would need a fence on the miter gauge and clamp the workpiece to the fence. Be sure that clamp face on the trailing edge is above the bottom face of the workpiece so it won’t catch on the edge of the table.

A big sled would also work if you rigged up some indeed support.