Absorbed Dose Resulting from a Specially Designed Computed Tomography Technique for Examination of the Urinary Bladder

Abstract

The absorbed spatial dose distribution resulting from a specially designed CT protocol for examination of the urinary bladder has been investigated with TLD rods in a body phantom containing tissue equivalent material. The CT examination consisted of scout view and both pre- and postcontrast scan series with 5 mm slice thickness and 5 mm unscanned intervals between successive scans. Cross-sectional dose distribution for one scan in the plane of the ovaries was measured as well as the dose profile for one scan along a line through the ovary parallel to the axis of rotation. Based on these measurements, the dose resulting from the whole CT examination was calculated, both with contiguous and noncontiguous scans. The ovarian dose was calculated for different positions of the ovaries in relation to the scanned area. The absorbed dose varied between 8.3 mGy and 9.7 mGy with the actual technique used. When contiguous scans with the same thickness were taken, the ovarian dose increased with a factor from 1.7 to 1.9. The dose resulting from the CT protocol of the urinary bladder was of the same magnitude as absorbed dose resulting from urography. When the diagnostic gain from a precise definition of tumor extent was taken into account, the dose resulting from the CT protocol was judged acceptable.