Typical diagnostic reference levels for common indications for computed tomography scans among adult patients in Kampala

Abstract

Background: As the number of CT scan examinations performed in Uganda has increased tremendously so has the medical exposure to ionizing radiation along with the risk of developing cancer. The ICRP recommends Indication Based Diagnostic Reference levels (IB-DRLs) as an effective tool that aids in optimizing CT scan radiation doses to minimize the harmful effects of ionizing radiation. The central region of Uganda which hosts Kampala, is a host to the highest number of CT scanners (13/25) in the country, lacks IB-DRLs to support optimization of the CT radiation doses employed for common CT scan indications among adults. Specific Objectives: To determine the facility reference levels for head trauma, acute stroke, interstitial lung diseases, pulmonary embolism, abdominopelvic lesions and urinary calculi in terms of CTDIvol and DLP at each selected hospital; To compute the typical DRLs for head trauma, acute stroke, interstitial lung diseases, pulmonary embolism, abdominopelvic lesions and urinary calculi in terms of CTDIvol and DLP at all three hospitals. Methodology: This was a cross sectional study design. Participant informed consent was obtained, and participant recruitment was by systematic sampling. 20 participants were recruited for each indication at a hospital to determine the facility reference levels for the common CT indications. A total sample size of 337 adult participants were recruited in the study to determine the typical DRLs for the common CT scan indications. Data analysis used descriptive statistics to determine the facility reference level and typical DRL of each indication as a median value of the average CTDIvol of the whole examination and median value of the total DLP of the whole examination. Additionally, an overall DRL for each indication was calculated as the 75th percentile of the median CTDIvol values and the median DLP values from the three hospitals for comparison to DRLs at 75th percentile from other studies. Results: The developed facility reference levels (FRLs) at three selected tertiary hospitals and the typical DRLs for the common CT indications among adult patients were as follows. The developed facility reference levels for acute stroke were 30.73mGy and 672mGy.cm at hospital A; 28.32mGy and 780mGy.cm at hospital B; and 30.14mGy and 608mGy.cm at hospital C. The developed typical DRL for acute stroke was 30.17mGy and 653mGy.cm. The developed facility reference levels for head trauma were 33.9mGy and 999mGy.cm at hospital A; 27.26mGy and 831mGy.cm at hospital B; and 32.9mGy and 813mGy.cm at hospital C. The developed typical DRL for head trauma was 32.04mGy and 878mGy.cm. The developed facility reference levels for interstitial lung diseases (ILD)/HRCT were 8.23mGy and 295mGy.cm at hospital A; 4.16mGy and 162mGy.cm at hospital B; and 3.28mGy and 109mGy.cm at hospital C. The developed typical DRL for ILD/HRCT was 4.66mGy and 161mGy.cm. The developed facility reference levels for pulmonary embolism (PE) were 7.0mGy and 610mGy.cm at hospital A; 5.02mGy and 252mGy.cm at hospital B; and 2.85mGy and 72.1mGy.cm at hospital C. The developed typical DRL for the whole examination of pulmonary embolism including precontrast and postcontrast sequences were 5.03mGy and 273mGy.cm. The developed facility reference levels for abdominopelvic lesion (ABDPL) were 10.45mGy and 1701mGy.cm at hospital A; 6.76mGy and 770mGy.cm at hospital B; and 5.19mGy and 668mGy.cm at hospital C. The developed typical DRL for abdominopelvic lesion (ABDPL) was 6.93mGy and 838mGy.cm. The developed facility reference levels for urinary calculi (UC) were 10.63mGy and 1903mGy.cm at hospital A; 6.89mGy and 855mGy.cm at hospital B; and 3.69mGy and 563mGy.cm at hospital C. The developed typical DRL for urinary calculi was 7.61mGy and 975mGy.cm. Conclusion: The developed typical IB-DRLs are recommended for use to manage CT radiation dose in Kampala. There was significant variation in the FRLs for most indications between most hospitals due to difference in imaging protocols /scan parameters used during the CT examinations. Recommendation: There is need to develop CT examination protocols that are optimized for specific clinical indications at hospital and national level to reduce variation in the scan parameters used to perform the examinations. IB-DRLs should be developed for the selected CT indications using data from more hospitals or CT imaging facilities in Kampala and update them every 3-5 years.