Eye lens dose in cranial computed tomography with reference to the technical development of CT scanners

The continuous technical development of cranial CT and the accumulation of clinical experience with this method, have resulted in the use of an increasing number of scan protocols for different clinical situations. An investigation was undertaken to find out how this change has influenced the dose delivered to the patient. The eye lens dose was measured at CT examinations in 245 patients, with appropriate scan protocols, and also at corresponding examinations in an anthropomorphic head phantom. One CT scanner of early (EMI CT 1010) and one of modern design (Siemens Somatom DR2) were investigated. The range of the eye lens dose was wide, namely 4 to 206 mGy for EMI CT 1010 and 6 to 124 mGy for Somatom DR2. In patient groups with comparable scan protocols the mean eye lens dose was higher with the Somatom DR2, mostly on account of a different spatial distribution of the dose in the scan plane. The dose varied less with this scanner, however, mainly because of the possibilities for more accurate positioning.