1. A method for performing a region growing comprising: identifying a first seed voxel; comparing a Hounsfield unit value of voxels adjacent to the first seed voxel with a threshold Hounsfield unit value for air; identifying the adjacent voxels as seed voxels, when each of the adjacent voxels meets or exceeds the threshold Hounsfield unit value for air; determining whether the identified adjacent voxels are a leakage object; segmenting newly identified adjacent voxels, which are determined not to be a leakage object; iterating the identifying, determining, and segmenting steps; determining whether a new adjacent voxel is segmented in a previous iteration; determining whether a leakage object is identified in the previous iteration when no new adjacent voxel is determined to have been segmented in the previous iteration, wherein leakage is determined based on (a) an inversely proportional relationship of a front size of adjacent voxels and an iteration number and (b) a linear relationship between the front size and bifurcations and changes in an airway shape; and reducing the threshold Hounsfield unit value and performing the region growing algorithm only on the identified adjacent voxels, as seed voxels, in the previous iteration when at least one leakage object is determined being identified in the previous iteration, wherein the method is performed by a processor.