Evaluation of the orientation dependence of optically stimulated luminescence dosimeters in computed tomography dosimetry using an anthropomorphic phantom under clinical imaging conditions

Objective: Small dosimeters such as optically stimulated luminescence dosimeters (OSLDs) and thermoluminescence dosimeters (TLDs) are used in anthropomorphic phantoms to measure actual organ exposure in X-ray computed tomography (CT) examinations. Nagase-Landauer currently supplies nanoDot dosimeters that employ OSLDs. The flat structure of nanoDot dosimeters causes their sensitivity to fluctuate according to the direction of the incident X-rays. We evaluated the effect of OSLD angle on measured values when dosimeters were placed within an anthropomorphic phantom and dosimetry was performed to mimic X-ray CT examinations. Methods: The dependence of OSLD placement angle on measured values was evaluated at eight points in the thorax and abdomen of the anthropomorphic phantom including the lung field, near the center of the phantom, near the body surface, and near the tissue boundary. Results: The system error for OSLDs positioned at different angles in the anthropomorphic phantom was 6.58%. Variation of measured values with the OSLD placement angles in the phantom resulted in errors ranging from –7.3% to +5.4%. Conclusion: Placement angle had little effect on measurement values when system error was considered. Therefore, it is not necessary to consider placement angle when measuring organ doses using OSLDs.