1. A non-transitory computer-readable medium embodying a program of instructions executable by machine to perform steps for localizing an anatomical structure, the steps comprising: (i) receiving a learned regressor and image data of a subject; (ii) invoking the learned regressor to predict a first distance from a seed voxel to a target anatomical structure in the image data based on appearance features of the seed voxel; (iii) selecting candidate voxels in the image data located at the first distance from the seed voxel; (iv) invoking the learned regressor to predict second distances from the candidate voxels to the target anatomical structure based on appearance features of the candidate voxels; (iv) in response to a smallest second distance being less than a predetermined threshold, outputting the candidate voxel associated with a smallest second distance as a localized voxel; and (v) in response to the smallest second distance being more than the predetermined threshold, setting the seed voxel to the candidate voxel associated with the smallest second distance and repeating at least steps (ii), (iii) and (iv).