1. A computer-implemented method of local surface smoothing of a three-dimensional (“3D”) binary volume of interest (“VOI”), wherein the VOI comprises a plurality of 3D surface points, the method comprising: identifying a projection plane; obtaining a two-dimensional (“2D”) projection image by projecting the plurality of 3D surface points onto the projection plane; determining a plurality of intensities of the projection image, the plurality of intensities comprising distances from the plurality of 3D surface points to the projection plane; identifying a bump region on the 2D projection image, wherein the plurality of 3D surface points comprises points outside and around the bump region and points inside the bump region, and wherein the plurality of intensities comprises intensities of the points outside and around the bump region and intensities of the points inside the bump region; obtaining fitted function values by fitting a third order polynomial to the intensities of the points outside and around the bump region; replacing the intensities of the points inside the bump region with the fitted function values; and projecting the fitted function values inside the bump region on the 2D projection image back to the 3D VOI.