Dose distribution, integral dose and radiation risk in computerized tomography of the skull

Abstract

The dose distribution and the integral dose for CT-examinations of the skull can be obtained experimentally from a three-dimensional array of TL-dosimeters in a tissue-equivalent phantom. In this paper we propose a new method which is based on two measured dose profiles for a single scan: f(z) along the central body axis z, and f(x,y) in the x-y plane perpendicular to z and parallel to the single phantom slices. Both dose profiles were measured with Harshaw TLD 100 rods and ribbons in an Alderson phantom in supine position. The computer — aided superposition of both dose profiles allows us then to reconstruct the spatial dose distribution and to compute the integral dose for any combination of scans. The application of this method is illustrated for a standard brain examination consisting of 14 scans adjacent to each other with a FWHM of the beam profile of 9 mm. The validity of this procedure was checked by comparing the theoretical reconstruction with TL-measurements revealing excellent agreement between calculation and experiment.