シンチレーション・ポイント線量計によるX線CT被曝線量の精密測定

抄録

A highly sensitive dosimeter with a small scintillation probe was devised for precise dosimetry of CT exposure. The probe, which was constructed using a small plastic scintillator and optical fibers coupled with photo-multipliers, had the advantages of directional and dose-rate independence of sensitivity on incident x-rays. Sensitivity, however, increased with x-ray effective energy, having a rate of 10% / 10keV at 50keV. The scintillation probe was placed on the surface and in the center of a human chest phantom with elliptical cross-section that was constructed using tissue-equivalent materials, and dose profiles were measured over a 300 mm scan width using a Toshiba TCT300 conventional scanner. Multiple scan average doses(MSADs)were estimated from the dose profiles as a function of the number of scans, and it was found that they were not saturated for the maximum number of 30 scans with a 10 mm slice and 10 mm distance between scans. Absorbed doses on the phantom's surface differed according to the position of the surface, where doses on the top were about 1.7 times larger than those on the side. MSADs estimated for the 30 scans on the top and side surfaces and in the center were 33.0, 19.6, and 34.1mGy, respectively, with maximum MSAD at the center of the phantom.