1. A computer readable medium embodying instructions executable by a processor to perform a method for generating a volumetric mask, the method comprising: providing a closed surface mesh; determining a discrete volume representation of the closed surface mesh; determining a temporary surface mask based on the closed surface mesh and a slice direction chosen from the discrete volume representation to produce a contour of the closed surface mesh for each slice of the discrete volume representation; and filling a surface defined by the contours to generate the volumetric mask, wherein the volumetric mask is output to one of a display and a memory.