P117] Dose estimation of eye lens for pediatric inner ear X-ray diagnosis

Abstract

Purpose Recently, digital X-ray tomosynthesis using flat panel detectors (FPD) has been used to diagnose the inner ears of pediatric patients. This imaging provides intermediate functionality between X-ray photographs and X-ray computer tomography (CT) scans. However, during inner ear diagnosis, digital X-ray tomosynthesis includes the eye lens in its field of view; an organ sensitive to X-ray doses. The purpose of this research is to evaluate the X-ray dosage upon the eye lens during inner ear diagnosis using digital tomosynthesis and to compare this dosage with X-ray CT exposure. Methods Small optically stimulated luminescence (OSL) dosimeters (nanodot: Nagase Landauer, Ltd.) were positioned on the eye lens of a phantom and on the bed of an X-ray TV device to measure the kinetic energy released per unit mass of air (air kerma). We performed tomosynthesis, assuming the conditions for an inner ear examination of an infant. The irradiant conditions were a tube voltage of 60–110 kV, an added filter of 0.1 mmCu, a swing angle θ of ± 20 °, and 76 photographs of a flame. The absorbed dose for the eye lens was calculated using the mass energy absorption coefficient ratio of the eye lens and air. In addition, the eye lens absorbed dose was compared with an X-ray CT scan. Results As the tube voltage increased, the absorbed dose increased. Moreover, when placed in a posterior-anterior (PA) position, as the phantom thickness increased, the absorbed dose decreased. On the contrary, when in an anterior-posterior (AP) position, as phantom thickness increased, the absorbed dose increased. Conclusions The eye lens absorbed dose in the PA position decreased by 90% compared to AP-positioning when using digital tomosynthesis for inner ear diagnosis of pediatric patients. Additionally, the eye lens absorbed dose in PA-positioned digital tomosynthesis decreased 93% compared to X-ray CT scans. Therefore, it is useful to reduce the exposure dose of the eye lens during inner ear diagnosis of pediatric patients via the use of digital tomosynthesis imaging.