Estimation of fetal S-value for various gestational ages from Positron-emitting radiopharmaceutical

Dosimetry of a pregnant woman under diagnostic imaging with ionizing radiation is very important due to the high radiosensitivity of the fetus and the destructive effects of radiation on it. In this study, the amount of S-values induced by the positron-emitting radiopharmaceutical 18F-FDG in different fetal organs were calculated using the MCNPX2.6 Monte Carlo code. In the simulations, hybrid phantoms of 3- 6- and 9-month pregnant women were used. The results showed that with increasing the fetal age, the self S-values of fetal organs decrease. A comparison between the calculated data in this study and those reported by other studies showed similar trend, however in some cases the data difference was up to 40% on average. These differences are due to the differences between the geometry of the used phantoms. Therefore, in order to more accurately estimate the dose to pregnant patient and her fetus, we intend to introduce a method for constructing a patient-dependent phantom using a limited number of measurements in our future studies, and thus increasing the accuracy of the calculated dose.