Organ doses for reference adult male and female undergoing computed tomography estimated by Monte Carlo simulations

Purpose: To develop a computed tomography(CT)organdose estimation method designed to readily provide organdoses in a reference adult male and female for different scan ranges to investigate the degree to which existing commercial programs can reasonably match organdoses defined in these more anatomically realistic adult hybrid phantoms Methods: The x-ray fan beam in the SOMATOM Sensation 16 multidetector CT scanner was simulated within the Monte Carloradiation transport codeMCNPX2.6. The simulated CT scanner model was validated through comparison with experimentally measured lateral free-in-air dose profiles and computed tomography dose index(CTDI) values. The reference adult male and female hybrid phantoms were coupled with the established CT scanner model following arm removal to simulate clinical head and other body region scans. A set of organdose matrices were calculated for a series of consecutive axial scans ranging from the top of the head to the bottom of the phantoms with a beam thickness of 10 mm and the tube potentials of 80, 100, and 120 kVp. The organdoses for head, chest, and abdomen/pelvis examinations were calculated based on the organdose matrices and compared to those obtained from two commercial programs, CT-EXPO and CTDOSIMETRY. Organdose calculations were repeated for an adult stylized phantom by using the same simulation method used for the adult hybrid phantom. Results: Comparisons of both lateral free-in-air dose profiles and CTDI values through experimental measurement with the Monte Carlo simulations showed good agreement to within 9%. Organdoses for head, chest, and abdomen/pelvis scans reported in the commercial programs exceeded those from the Monte Carlo calculations in both the hybrid and stylized phantoms in this study, sometimes by orders of magnitude. Conclusions: The organdose estimation method and dose matrices established in this study readily provides organdoses for a reference adult male and female for different CT scan ranges and technical parameters. Organdoses from existing commercial programs do not reasonably match organdoses calculated for the hybrid phantoms due to differences in phantom anatomy, as well as differences in organdose scaling parameters. The organdose matrices developed in this study will be extended to cover different technical parameters, CT scanner models, and various age groups.