Abstract:
Rationale: Population exposure to ionizing radiation from medical imaging has been an important concern for decades. With the number of computed tomography (CT) scans performed in Quebec growing by 204 % in the very last decade, it is essential to ensure that CT protocols are optimized. Main
Objective: The final goal of this study, beyond the scope of this article, is to establish provincial diagnostic reference levels (DRLs) for Quebec with the purposes of: 1) optimizing imaging protocols so as to minimize patient exposure to ionizing radiation while maintaining sufficient image quality for diagnosis and thus 2) reduce the population's exposure to ionizing radiation. This investigation is called Q-DRL-P, meaning “Quebec-DRL-Project”.
Specific Objective: These preliminary data, reported here, aim to highlight the utility and relevance of periodic review of CT protocols; this is a basic feature included in Q-DRL-P.
Materials and Methods: This study began in early 2022. We evaluated patient exposure to ionizing radiation from two highly technologically categorized CT scanners (CTSc-1 and CTSc-2), located in the same facility (Facility-X), for CT examinations of the chest. In total, from 2017 to 2024, 2,480 women and 3,808 men (total of 6,288 patients) were examined with CTSc-1 (5,074 examinations) and CTSc-2 (1,214 examinations), for a total of 6,288 CT exams. We analyzed separately and respectively the CTSc-1 exposure data of women (70 ± 13 years) and men (69 ± 12 years), as well as the CTSc-2 exposure data of women (70 ± 12 years) and men (69 ± 12 years), from the year 2020 until the beginning of 2022. This first analysis showed that CTSc-2 overexposed men patients by an average of 134%, compared to CTSc-1 (DLP of 273 mGy.cm vs 117 mGy.cm). Equivalently, women patients were also found to be overexposed to the extent of 104% (DLP of 188 mGy.cm vs 92 mGy.cm). This led Facility-X to contrast the “Chest protocol” of the CTSc-1 scanner with that of the CTSc-2.
Results: Overexposure to CTSc-2 was found to be due to over-optimization of “Reference Quality Imaging,” which is the strategy used to achieve automatic exposure control (AEC) in modern CT scanners. This has been adjusted accordingly and appropriately. We then compared the pre-adjustment data with 24-month post-adjustment data. For women and men, respectively, no statistically significant difference was observed for somatic data (age, weight and height) between the pre- and post-adjustment periods. In contrast, CTSc- 2 shows an exposure reduction of 46% for men and 33% for women. Furthermore, no significant qualitative and quantitative differences were observed in terms of image quality for CTSc-2 before and after adjustment in the CT Chest protocol.
Discussion and Conclusion: Current technologies have significantly improved the performance of CT scanners. On the other hand, as in Quebec, the number of CT examinations is experiencing impressive growth throughout the world. Our results showed and confirmed that patient exposure to radiation can be reduced while maintaining good image quality that is suitable for the intended diagnostic purposes; this is consistent with the ALADA principle which states “As low as the diagnostically acceptable”. These results also support the current global movement to optimize patient exposure to radiation in medical imaging
