## 4 Discussion
Similar findings to those in CT for abdominal pain were found in CT for polytrauma (Figure 2). The dose ranged from 15.9 mGy to 47.4 mGy when all hospitals and all eight CT units were taken into account. These differences are mainly due to different protocols with different numbers of phases used (Table 3). This was expected since a whole-body tomography scan is performed in various protocols and there is no agreement as to which protocol is optimal in an emergency situation [34,35]. An unenhanced scan is sometimes built into the protocol [36,37], but the Royal College of Radiologists [38] is of the opinion that an unenhanced scan of the body is of no benefit to polytrauma patients. Nevertheless, a narrower range of fetal doses was found in polytrauma than in abdominal CT within the same hospitals. This is due to the similar CT protocols used within one hospital for polytrauma, while for abdominal CT, protocols differed in doses per phase, but also in the number of phases (Table 3). This again shows the need for the optimization and harmonization of radiological practice. The results presented in this study are always below 100 mGy, which is the threshold for deterministic effects indicated by the International Commission for Radiation Protection [14]. Nevertheless, in the case of repeated CT procedures of the abdomen or additional phases used, fetal doses could reach higher values that could lead to possible deterministic radiation effects on the fetus. Since different clinical scenarios justify the use of the aforementioned diagnostic procedures, especially in the case of scarce diagnostic information gained from ultrasound examination and/or the inadequacy of magnetic resonance imaging [12,13], it is important to use well-optimized imaging protocols. This underlines another finding of this study: large variability in fetal doses for the same procedures between different hospitals, but also within the same hospital. Besides large fetal dose differences, this can also imply significant differences in diagnostic information obtained. Although the fetal risk of developing malignant disease in childhood is small, it can be changed using different protocols, which raises the importance of the implementation of strategies for reducing radiation exposure, without compromising the quality of diagnostic data obtained [19]. Through using the freely available, inexpensive physical phantom, Tena, developed by our group [23,24], fetal dosimetry data in diagnostic imaging procedures were further improved. Additionally, the fetal dose dependance of imaging protocols was confirmed. Nevertheless, exposure of the fetus also depends on the gestational age, maternal body habitus, and fetal depth. In addition, a fetus in the second trimester can freely move within the placenta, and there is a possibility that the radiation dose for fetuses in the cephalic position could differ for different positions. For this reason, further studies of fetal dose for differently constructed phantoms and acquisition parameters are needed. Patient doses in diagnostic and interventional radiology procedures are optimized, and in most imaging modalities, reduced nowadays. This calls for repeated measurements of patient doses. The results presented in this work could help to better understand the radiation safety of pregnant patients and improve radiation protection measures and the optimization of imaging procedures for pregnant patients. The obtained data contribute to the general knowledge of fetal doses during diagnostic and interventional radiology procedures and to the prevention of unnecessary delays in providing the necessary procedures in pregnancy. Additionally, the presented variability in fetal doses for the same procedures highlights the need for the improved optimization of imaging protocols. Conceptualization, D.F., A.T. and V.K. ; methodology, H.B., I.K., M.K., Z.K., M.M., M.H. and T.T. ; validation, I.B. and M.S. ; formal analysis, D.F. and Z.M. ; investigation I.B., I.K., F.D.M., N.Z. and R.L.