SU-F-207-10: Simulation Study of Patient Off-Centering Effect On Organ Dose in Chest CT Scan

Purpose: To simulate off-center chest CT scans on adult phantoms and to determine the impact on organ dose. Methods: A GPU-based fast Monte Carlo code ARCHER was used for simulation of chest CT scan on RPI-adult female (RPI-AF) and RPI-adult male (RPI-AM) phantoms. A CT scanner model of GE LightSpeed Pro 16 previously developed was simulated with a fixed 200 mAs per rotation. The human phantom was placed in supine posture at the isocenter of CT model to generate organ doses for the “centered” case. Off-center table positions were simulated by moving the phantom towards and away from the 12 o’clock position on the CT model. A 5cm change in either direction of table height change was simulated in 1 cm increments. Organ doses were calculated at each table height, and compared to determine the effect of off-centering on dose. Results: Breast dose for female adult phantom changed the most with position by up to 25%, where lower position increased breast dose and higher position decreased it. The thymus shared the same trend as the breasts, with total dose change of 17% for male adult phantom. The adrenals, which were near the back surface of phantom, had a dose trend opposed to the breasts that decreased at lower position and increased at higher position. The lungs, which were large organs in chest cavity near body center, were only slightly affected by off-centering with 4% decrease in dose at most. Conclusion: Organs at or near body surface were affected most by off-centering. Lower table height increased dose to the breasts and thymus. Higher table height increased dose to the adrenals. This study confirmed the results found in physical phantom measurements. National Institutes of Health R01EB015478