In the present study, a high-quality voxel model of a Korean adult male was converted to a surface model based on polygon and nonuniform rational B-spline surfaces. The polygon model of the body surface was then modified in the back and buttock regions for some correction and finally converted back to a voxel model for Monte Carlo dose calculations. The dose calculation results showed that the modification of the back and buttock significantly changed the calculated dose values of the lungs and breasts for the postero-anterior irradiation geometry; the maximum difference, found for the lungs, was as large as 40% for the photon energy of 30 keV, even though the difference decreases with the photon energy.