Purpose: Computational anthropomorphic phantoms represent human body using mathematical or voxelized description. The voxel phantom, which was modeled in tomography images of a human, consists of shape, material and mass of the human body composition. It can be used in calculating organ dose of humans. In this study, we develop the voxel head phantom on the basis of computed tomography (CT) image, and calculate organ doses using MCNPX simulation code and the voxel head phantom to evaluate the radiation dose delivered using a conventional and a novel periapical radiography. Methods: The voxel head phantom is developed based on CT images of RANDO phantom (The Phantom Laboratory, Salem, NY) designed to have the same absorption as human tissue at the radiography exposure levels. The voxel head phantom is constructed with bone, air and soft tissue applied through brightness levels of CT images. The Organ doses are calculated in head structures, such as bone marrow, thyroid, salivary gland, oesophagus, brain, skin and eye. To verify calculated doses, the calculated dose values are compared with measured dose values using dosimeters and a fabricated QA phantom for dose measurement. Results: A novel periapical radiography has lower absorbed doses than a conventional periapical radiography at head organs excepting the sublingual gland. And, the differences between the calculated dose values and the measured dose values are within 20 % according to the exposure energy and the depth of penetration. Conclusion: The voxel phantom and the procedure for calculating radiation doses using MCNPX simulation code are useful tools for detecting the absorbed organ dose, which cannot be measured directly in patients.