An analysis of the vortex
A dimensional radius is a central component to a spatial vortex, defining the vortex's strength and ability to sustain a passageway through space.
In 2375, the crew of the USS Voyager discovered a spatial vortex in the Delta Quadrant, being used by the Malon to dump antimatter waste in a starless area of space known as "the Void." As the Malon's activities were severely damaging the health of the Void's only native inhabitants, Captain Janeway developed a plan whereby photon torpedoes would be utilized to destroy the vortex. Doing so, however, would require collapsing it from the end of the vortex located in the Void, where the vortex's dimensional radius was weakest.
Since this act would effectively strand Voyager in the Void, the crew modified the plan to deploy the torpedoes immediately upon entering the vortex, then jumping into high warp to outrun the shock wave. (VOY: "Night")