Abstract
Detailed knowledge about radiation exposure is crucial for radiology professionals. The conventional calculation of effective dose (ED) for computed tomography (CT) is based on dose length product (DLP) and population-based conversion factors (k). This is often imprecise and unable to consider individual patient characteristics. We sought to provide more precise and individual radiation exposure calculation using image based Monte Carlo simulations (MC) in a heterogeneous patient collective and to compare it to phantom based MC provided from the National Cancer Institute (NCI) as academic reference. Dose distributions were simulated for 22 patients after whole-body CT during Positron Emission Tomography-CT. Based on MC we calculated individual Lifetime Attributable Risk (LAR) and Excess Relative Risk (ERR) of cancer mortality. EDMC was compared to EDDLP and EDNCI. EDDLP (13.2 ± 4.5 mSv) was higher compared to EDNCI (9.8 ± 2.1 mSv) and EDMC (11.6 ± 1.5 mSv). Relative individual differences were up to −48% for EDMC and −44% for EDNCI compared to EDDLP. Matching pair analysis illustrates that young age and gender are affecting LAR and ERR significantly. Because of these uncertainties in radiation dose assessment automated individual dose and risk estimation would be desirable for dose monitoring in the future.
Highlights
Are calculated on these imprecise data could be misinterpreted
Whole body computed tomography (CT) from combined Positron Emission Tomography (PET)-CT examinations were exclusively selected in order to minimize the indeterminate radiation dose to body parts outside the imaging volume that cannot be assessed by Monte Carlo (MC)
Individual radiation dose assessment and risk calculation is feasible by image based Monte Carlo simulations and organ segmentations in an adult clinical routine collective that underwent full body exposure in a single spiral acquisition
Summary
Conventionally calculated EDDLP can be used for comparison between different CT-scanners or different examination protocols, but should not be used for comparison between different patient collectives or for radiation risk estimation[8,9]. Huda et al were able to show that this phantom based technique is feasible to derive organ doses and to use these for cancer risk estimation[11]. The authors of BEIR VII report follow the linear Non-threshold Dose-Response Model and presume that the risk of cancer incidence and mortality due to medical examinations are mainly based on low-level ionizing radiation dose, age and gender[14]. The aim of this study was to provide individual calculations of ED in whole-body exposure derived from MC calculations (EDMC) and to compare them with the conventional method (EDDLP) and the academic reference (EDNCI) following an equivalence hypothesis in a heterogeneous study collective. Whole body CT from combined Positron Emission Tomography (PET)-CT examinations were exclusively selected in order to minimize the indeterminate radiation dose to body parts outside the imaging volume that cannot be assessed by MC
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