Evaluation and Validation of Computed Tomography Dose Accuracy (Ctdiw and Ctdivol)

Abstract

Weighted and average dose within a scan volume of a phantom have been evaluated and validated using two different devices and techniques. The Barracuda electrometer and Ion Chamber techniques were applied on a 16 slice Siemens CT scanner and the results compared to the console displayed CTDIw and CTDIvol valuesfor accuracy and compared to each other for validation purposes. With fixed exposure parameter of 130kVp and varying tube current-time products from 140mAs to 300mAs for the CT head phantom examination, there were varying deviations in both the CTDIw and CTDIvol from the two techniques. Tube currents of 140 mAs, 240 mAs and 300 mAs yielded 3.5%, 0.61% and -6.45% deviations when the respective CTDIvol values for both techniques were compared. There were mean CTDIvol of (42.3 + 8.6) mGy and (42.1 + 8.1) mGy for Barracuda and Ion Chamber techniques respectively with an average deviation of 1.4 mGy between them, when the tube currenttime products were varied from 140 – 300 mAs for the head phantom examination. Tube current-time products ranging from 80mAs – 220mAs were used for the CT body phantom examination and mean CTDIw measured were (16.6 + 6.7) mGy and (16.5 + 7.7) mGy for Barracuda and Ion Chamber techniques respectively with an average deviation of 1.0 mGy between them. The estimated head and body dose deviations were compared to international dose accuracy range. The results of the study showed that the deviations from the techniques were within a range of CTDIw and CTDIvol values which were favorably comparable to other similar retrospective research works, thus, the Ion Chamber technique can be used in place of the technique currently in use.