1. A method for segmenting a polyp in a computer tomography colonography (CTC) volume, comprising: receiving an initial polyp position in a CTC volume; detecting a polyp tip in a neighborhood of the initial polyp position; fitting a local polar coordinate system to a colon surface in the CTC volume based on the detected polyp tip, the local polar coordinate system including a plurality of axes; detecting polyp interior and polyp exterior voxels along each of the plurality of axes of the local polar coordinate system; and segmenting a boundary of a polyp in the CTC volume by detecting a boundary voxel for each of the plurality of axes of the local polar coordinate system based on the detected polyp interior and polyp exterior voxels.