1. A machine for performing image segmentation of images of anatomical structures or organs, comprising: a processor or microprocessor coupled to a memory, wherein the processor or microprocessor is programmed to perform image segmentation by: acquiring 3-dimensional image data for an organ or anatomic structure; selecting a 2-dimensional seed image slice from the 3-dimension image data; delineating a target on the seed image slice, the target comprising the organ or a portion of the organ; selecting a 2-dimensional neighboring image slice adjacent or near to the seed image slice; automatically generating a deformation field through deformable image registration conducted between the seed image slice and the neighboring image slice; and obtaining a delineation of the target on the neighboring image slice by applying the deformation field onto the delineation of the target on the seed image slice.