Evaluating Effective Dose: A Comparison of Methods Based on Organ Dose Calculations versus Dose-Length Product and Monte Carlo Simulation

Computed tomography (CT) has had a massive impact on diagnostic radiology over the past few decades. Serious concerns exist because of the increase in the effective radiation dose associated with CT scans, which could pose significant health risks. In CT, the effective dose can be estimated by Monte Carlo simulations. The aim of the study was to estimate and compare the effective doses for CT from organ dose-based calculations using the tissue weighting factors of the International Commission on Radiological Protection publications (ICRP 60, 103), Monte Carlo CT-Expo v2.6, and dose-length product (DLP)-based estimates. For 165 CT scans, the effective doses (Ed) of the most common routine radiological investigations were assessed. There were 112 male patients (68%) and 53 female patients (32%). When compared to organ dose-based estimates, the DLP-based estimates of the effective dose produced by applying ICRP 60 coefficients were less than 55–57% (head) and more than 18.1% (chest) and 20% (abdomen). The ICRP 103 values of the Ed were less than 79% (head) and more than 17% (chest), and they changed randomly with the tissue weighting factors for the abdomen. For Monte Carlo CT-Expo, the Ed values were lower by 54% (head), 6% (abdomen), and more than 2% (chest) compared to organ dose-based estimates. Effective doses calculated using the tissue-weighting factors of ICRP 103 values comparable to ICRP 60 differ greatly by an average of 2.3, 2.9, and 4.5 mSv for the head, chest, and abdomen, respectively. In conclusion, all estimates of Ed are subject to the biases inflicted by the assumptions in the methods used; therefore, no significant agreement should be expected. The reason for evaluating ICRP 60 is to make a point that ICRP’s update is indeed more accurate. The variability associated with the use of various methodologies to estimate and compare the effective dose Ed in CT scans was shown to be significant in this study.