Development of size-specific dose estimates for common computed tomography examinations: a study in Ghana

This study determined the size-specific dose estimate (SSDE) of computed tomography (CT) examinations and derived mathematical expressions for dose output estimation and optimization in a teaching hospital in Ghana. Demographic and scanner output indices, including CT dose index (CTDIvol) and dose length product for adult head, chest and abdominopelvic (ABP) CT examinations carried out at the hospital from 2018 to 2020, were retrieved from the picture archiving and communication system of the CT scanner machine. Other indices such as the antero-posterior diameter (D (AP)), lateral diameter (D (L)) and diagonal diameter (D (dia)) of the patients' bodies were measured on the mid-slice axial image using a digital caliper. The effective diameter (D (eff)) was then calculated as the square root of the product of the D (AP) and D (L). The SSDEs were calculated as the product of the CTDIvol and the size-specific conversion factors obtained from Report 204 of the American Association of Physicists in Medicine. Regression analyses were performed to find the relationship between SSDE and the various parameters to derive mathematical equations for the dose estimations. There were more female samples (n= 468, 56.3%) than male samples (n = 364, 43.7%) for each CT procedure. The SSDEs and size-specific diagnostic reference levels (SSDRLs) were: head (83.9 mGy; 86.9 mGy), chest (8.1 mGy; 8.7 mGy) and ABP (8.4 mGy; 9.2 mGy). The variations between CTDIvol and SSDEs for head (2.50%), chest (25.9%), and ABP (26.2%) showed an underestimation of radiation dose to patients, especially in chest and ABP examinations, if CTDIvol is used to report patient doses. The SSDEs of the chest and ABP CT examinations showed linear correlations with the CTDIvol. The estimated values could be used to optimize radiation doses in the CT facility. The SSDE and SSDRLs for head, chest and ABP CT examinations have been developed at a teaching hospital in Ghana. The SSDEs of chest and ABP examinations showed linear correlations with the CTDIvol and hence can be calculated using the mathematically derived equations in the study.