Purpose: The aim of this study was to determine the mean volume computed tomography dose index (CTDIvol) for the standard head and body phantoms and locally designed head and body phantoms respectively. Similarly, this study determined and compared the displayed mean CTDIvol and Dose Length Product (DLP) for the above phantoms from the CT monitor. In addition, the percentage deviations of both phantoms were compared with the recommended limits from the International Atomic Energy Agency (IAEA) and the American College of Radiologists (ACR). Materials and Methods: Dose measurements were made using a standard polymethymethacrylate (PMMA) phantom for head and body as well as a locally designed phantom with four CT scanners using thermoluminescence dosimeters (TLDs). The locally designed phantoms were made using a PMMA sheet, which was bent to give the desired cylindrical shape and was made like the standard phantoms. The constructed phantom was filled with water and the TLD chips were inserted into the center and peripheries of the phantoms to obtain the absorbed doses. Results: The CTDIvol for the standard head and body phantom for center A was 66.97 and 21.85mGy and for B was 23.39 and 6.29mGy respectively. Similarly, the CTDIvol for the constructed head and body phantom for center A was 63.91 and 19.84mGy and for B was 24.67 and 6.30mGy respectively. The uncertainty between the standard and constructed head phantoms for centers A and B was 4.6 and 5.5% respectively, while that of the standard and constructed body phantoms for centers A and B was 9.2 and 0.0% respectively. The maximum percent deviation from the console CTDIvol and DLP values with the four phantoms for centers A and B was within ±20%. The mean correction factors for the head and body were 0.998 and 1.05 respectively. Conclusion: The uncertainties obtained in this study were within the IAEA and ACR recommended value of ±20%. The constructed phantom proved useful for CT dose measurements.

Context: Diagnostic reference level (DRL) is the first step in the optimization process to manage patient dose corresponding with the medical purpose. Aim: The objective of this study was to develop local DRL for computed tomography (CT) of the head and abdomen in adult patients in four CT centers in South-South Nigeria. Materials and Methods: A prospective, cross-sectional study of 546 adult patients that underwent CT examination of the head and abdomen from 2018 to 2020 using four different CT scanners. Volume CT dose index (CTDIvol) and dose length product (DLP) of contrast and non-contrast CT examinations of the head and abdomen were collated and the 50th percentile DRL was determined and compared to other published DRLs. Results: The 50th percentile CTDIvol/DLP for non-contrast head CT examination for centers A, B, C, and D was 75.3 mGy/1776.6 mGy.cm, 21.8 mGy/457 mGy.cm, 17.4 mGy/373.6 mGy.cm, and 29.6 mGy/628.5 mGy.cm, respectively. The 50th percentile CTDIvol/DLP for contrast head CT examination for centers A, B, C, and D was 150.6 mGy/3326.2 mGy.cm, 41.4 mGy/832.4 mGy.cm, 35.6 mGy/653.6 mGy.cm, and 77.9 mGy/1458.4 mGy.cm, respectively. The 50th percentile CTDIvol/DLP for non-contrast abdomen CT examination for centers A and B was 22.8 mGy/1488.5 mGy.cm and 7.9 mGy/302.3 mGy.cm, respectively. The 50th percentile CTDIvol/DLP for contrast abdomen CT examination for centers B and C was 19.6 mGy/825.7 mGy.cm and 31.5 mGy/1555.5 mGy.cm, respectively. There was correlation between contrast and non-contrast CTDI (P = 0.003) and DLP (P = 0.025) for the head. Conclusion: Wide variations CTDIvol and DLP values were observed among the centers for similar body part CT examinations.

Background The rising increase in the incidence of breast cancer among women is worrisome and a great concern to all. More disturbing is that the incidence of breast cancer and death has been attributed to exposure to imaging modalities that utilize ionizing radiation such as computed tomography. The aim of this study was to estimate the lifetime attributable risk (LAR) incidence and mortality for breast cancer for female patients who had head computed tomography in two imaging facilities (centres) in the Niger Delta region of Nigeria. Result The overall estimated mean effective dose in centres G1 and G2 is 5.76 mSv and 1.54 mSv, respectively. There was a statistical significant difference in the mean effective dose between centres G1 and G2 (P < 0.001). The LAR breast cancer incidence obtained in this study ranged between 0.5 and 26.45 per 100,000 population in centre G1, while in centre G2, it ranged between 0.14 and 6.56 per 100,000 population. The LAR breast cancer mortality obtained in this study ranged between 0.07 and 6.25 per 100,000 population in centre G1, while in centre G2, it ranged between 0.03 and 1.55 per 100,000 population. Conclusion The estimated mean LAR of breast cancer incidence and mortality for the women who had head CT examination in the two study centres was found to be minimal to negligible among the female patients of the different age groups in the study population. The overall mean risk of breast cancer incidence was very low in centre G1 and minimal in centre G2. The obtained risk values can be used to optimize the dose delivered to patients and also ensure that CT examinations are justified.