The effect of overranging on patient effective dose and organs' doses during parathyroid CT examinations utilising Monte Carlo software

Abstract

This study aimed to assess the influence of overranging on patient effective dose (ED) and radiosensitive organs' dose (OD) of adult patients undergoing two-phase parathyroid computed tomography (CT) examinations utilising Monte Carlo simulation and propose methods for elimination of its impact in clinical practice. The volumetric computed tomography dose index (CTDIvol), dose length product (DLP) per examination, demographic and anatomical data, as well as technical data were retrospectively recorded for seventy-six patients. The ED and OD values were calculated for both sexes and phases as well as a total, with and without considering overranging, using VirtualDoseCT software incorporating a Toshiba Aquilion Prime 80 (80-detector rows) CT scanner and the recorded parameters. A significant reduction of about 30% (Wilcoxon test p < 0.0001) was found in total ED values obtained without considering overranging (3.15 vs 4.17 mSv). A significant decrease was also found in total ODs without considering overranging for females (except for the thyroid), males, and patients’ total sample (Wilcoxon test, p < 0.05). The percentage differences in total ODs between the two methods were 2.1% for thyroid, 14% for oesophagus, 15% for thymus, 19% for eye lenses, 26% for lungs, and 84% for breasts. A non-significant decrease of 4.6% (Mann-Whitney test, p = 0.259) was found in total ED values obtained without considering overranging for males compared to females (3.12 vs 3.26 mSv). In addition, a significant reduction was found in total ODs for males compared to females for thyroid, oesophagus, and eye lenses (Mann-Whitney test, p < 0.0001), but not for breasts (Mann-Whitney test, p = 0.061), and a non-significant increase for the lungs and thymus (Mann-Whitney test, p > 0.05). Our results highlight that overranging should be of particular concern when optimisation strategies are planned during parathyroid CT imaging, since there is the potential to significantly reduce ED and OD absorbed by radiosensitive organs inside or adjacent to the scanning volume. Further work needs to be conducted, combining physical and technical parameters affecting overranging, to increase the awareness and understanding of the unnecessary patient dose during CT imaging, and motivate CT facilities to implement dose optimisation strategies.