During computed tomography (CT) examinations, radio -sensitive organs located outside the field of view (FOV) are usually exposed to radiation caused by both direct and scattered X-rays. Traditionally, the use of radi...
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During computed tomography (CT) examinations, radio -sensitive organs located outside the field of view (FOV) are usually exposed to radiation caused by both direct and scattered X-rays. Traditionally, the use of radiation protection products has been an option for reducing exposure doses. The catalog value of the dose reduction factor (DRF) for a commercial X-ray shield is generally determined by the manufacturer using a plain X-ray irradiation system to measure the difference in dose with and without the shield. In contrast, actual shielding ability measurements during clinical CT examinations are usually evaluated using a similar equation, but it is not guaranteed that the incident directions of Xrays will be the same between the measurement data with and without a shield. The purposes of this study are to introduce a novel method for evaluating DRF by accounting for the influence of the X-ray incident direction in helical scanning and to obtain knowledge about the correctness of previously reported DRF values. Experiments pertaining to chest CT examinations were performed using a human body phantom and small -type dosimeters which consist of an optically stimulated luminescence element using Al2O3:C. A total of 100 examinations were iteratively performed, both with and without a shield. The corresponding DRF was then calculated. The novelty of the proposed analysis procedure lies in a paired analysis method, where the DRF is calculated by reorganizing numerous acquired data sets with and without the shield to pair similar incident angles of X-rays. As a result, the DRF values were estimated to be 48.5 +/- 4.3%, 48.7 +/- 2.7%, and 48.9 +/- 1.5% based on the data results within the 10-40 data sets, 40-70 data sets, and 70-100 data sets, respectively. When the DRF values were obtained by the conventional method without applying our sorting procedure, the results were 48.4 +/- 8.1%, even when the 70-100 data sets were used. This result indicates that the proposed me
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