Voronoi cells are defined by neighborhood of entities (points, lines, circles, ...).
Therefore, the borders of Voronoi cells are defined by equidistant lines between entities.
1, between a pair of points, the equidistant line is a perpendicular bisector;
2, between a point (or a circle) and a straight line, the equidistant line is a parabola with the the point as focus and the straight line as directrix;
3, between two circles of distinct radii, the equidistant line is a parabola with focii at circle centers and major radius as half of the difference in radii;
4, we probably don't want to handle Voronoi by entities of ellipses/hyperbola/parabola. if we do, probably Bezier is the way to go. Then, we need to improve our Bezier.