Evaluation of the eye lens dose using preoperative three-dimensional computed tomography angiography and three-dimensional rotational angiography examinations in neurosurgery to prevent radiation hazards

This study had two objectives: 1) to accurately evaluate the radiation dose to the eye lens from preoperative examinations by using optically stimulated luminescence dosimeters (OSLDs), and 2) to determine how closely the dose metric reported on the scanner console (the volume computed tomography dose index [CTDI_vol] and the displayed air kerma values) matched the actual eye lens doses. Radiation doses measurements were made at a single hospital during three-dimensional (3D) computed tomography (CT) angiography (3DCTA) using a 64-row multi-detector CT scanner (Aquilion, Toshiba Medical System Corporation, Otawara, Japan) and 3D rotational angiography (3DRA) using an angiography unit (Innova IGS 630, GE Health-care, Milwaukee, WI, USA). The study parameters were identical to those used during clinical acquisition. For each protocol, the radiation doses were measured using five OSLDs, which were placed on the surface of a phantom on the right and left eye lenses, the right and left ears, and the occiput. The eye lens doses for 3DRA and 3DCTA were approximately 7 mGy and 70 mGy, respectively, at only one time. Using 3DRA, the highest dose was to the occiput and the lowest to the right eye, whereas with 3DCTA the highest dose was to the right eye and the lowest to the occiput. Using the CT scanner, the ratios from the cumulative CTDI_vol for the left and right eye lenses were 0.85 and 0.88, respectively. When using angiography, the radiation dose for each anatomical region was lower than the displayed air kerma value. The eye lens doses were lower for 3DRA than for 3DCTA because of the orbital rotation of the X-ray tube. During 3DRA, the X-ray tube is positioned behind the patient's head at approximately 240 degrees. The eye lens is within range in front of the patient's head by approximately 120 degrees. Conversely, 3DRA irradiation avoids the eye lens, which is not positioned within the range of the primary radiography beam. Comparisons between the displayed air kerma values and radiation doses for each anatomical region showed that the values did not match. Furthermore, the estimated value using the dose-area product was barely lower than the radiation doses for each anatomical region, except for the eye lens. As the eye lenses were not subjected to irradiation from the primary beam from the angiography unit, the eye lens doses and the estimated value (18.1 mGy) did not match. In conclusion, it is essential for physicians to monitor for cataract development in the eye lenses of patients who undergo examinations such as 3DCTA and 3DRA multiple times. (author)