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    Assessment of Diagnostic Reference Levels and Radiation-induced Lifetime Cancer Risk from Computed Tomograhpy Examinations in Selected south-western Nigerian Teaching Hospitals
    (2026-07-16) Olawuni Caroline Olayemi
    The growing utilisation of computed tomography (CT) has prompted greater attention to exposure of radiation and its potential health risk coupled with the lack of nationally established diagnostic reference levels (DRLs) in Nigeria. This study was therefore aimed at assessing DRLs and estimating lifetime attributable cancer risks (LAR) among population involved in CT examinations at the participated teaching hospitals in South-western Nigeria. A retrospective study was adopted using CT examination data obtained from two University teaching hospitals in South-western Nigeria; Babcock and Obafemi University Teaching Hospitals. CT records from 266 patients who underwent CT examinations were analyzed. CTDIvol and DLP were recorded directly from CT scanner and size-specific conversion factor published by Romanyukha et al. (2016) was used to estimate effective doses. 75th percentile value of CTDIvol and DLP was adopted as local Diagnostic Reference Levels (DRLs). LAR was estimated using online X-ray risk software. Data were analysed using IBM SPSS. The results showed considerable variability across anatomical regions and examination protocols, indicating a wide spread of patient doses. In centre A, the mean CTDIvol for non-contrast head examinations was 49.7±19.4 mGy, while contrast-enhanced head examinations recorded 69.7 ±32.8 mGy. Similarly, abdominal examinations showed substantial variation, with CTDIvol and DLP values of 31.3 ± 23.8 mGy and 1304.0 ± 905.9 mGy.cm respectively. In centre B, head examinations exhibited CTDIvol values of 58.5 ±19.4 mGy and DLP values of 1219.6 ± 431.0 mGy.cm. The adult local DRLs estimated for head CT showed CTDIvol values ranged from 57.6 – 65.3 mGy, while DLP ranged from 1393.5 – 2050.1 mGy.cm. Chest CT recorded CTDIvol values between 6.9 and 15.4 mGy while DLP recorded 495.6 and 819.0 mGy.cm. Abdomem examinations showed CTDIvol values 8.6 – 42.0 mGy and DLP values of 1621.9 – 1730.2 mGy.cm. some of the values recorded were within the ICRP recommended limits while some were greater than the ICRP CTDIvol and DLP values which are 60 mGy, 1050 mGy.cm, 30 mGy, 650 mGy.cm, and 35 mGy, 780 mGy.cm for head, chest, and abdomen respectively. Among pediatric patients, head CTDIvol (30.6 - 45.8) mGy were below the ICRP reference levels of 70 mGy. However, pediatric head DLP values reached 1515.4 mGy.cm in centre A and 872.9 mGy.cm in centre B, exceeding the recommended value of 750 mGy.cm. The lifetime cancer risk ranged from 10 to 275 cases per 100,000 population and the highest recorded in the study (275 cases per 100,000 population) was associated with contrast-enhanced CT examinations while the lowest LAR (10 cases per 100,000 population) was observed among patients > 60 years. The statistical test employed demonstrated significant differences in LAR across gender, age groups, region, and contrast status (P < 0 .001). CT examinations contributed significantly to patient radiation exposure and potential cancer risk, particularly when the recommended DRLs were consistently exceeded. Young patients, females, and patients that underwent contrast CT examinations exhibited LAR. Consequent to the findings, the study recommends establishment of separate national DRLs for adults, pediatrics, and contrast-enhanced CT examinations in Nigeria. Key Words: Cancer, Contrast-enhanced, Diagnostics, patient, pediatrics, Word counts: 493