Purpose: To provide updated radiation dose from diagnostic exams performed for pregnant patients suspected of pulmonary embolism (PE) using the recently developed BREP phantoms of pregnant woman and the fetus. Also to challenge the validity of current recommendations suggest that ventilation/perfusion (V/Q) single photon emission computed tomography (SPECT) vs. computed tomography pulmonary angiography (CTPA) should be considered for diagnosis of PE in radiosensitive groups such as pregnant women. Methods: The Monte Carlo calculations involving detailed geometrical simulation of pregnant women and the fetus were performed. Results: The results showed that when radiation dose to the fetus is of concern, CTPA is more appropriate at early stages of pregnancy causes 50 – 97 % lower fetal doses for the first two trimesters of pregnancy. While for gestational periods more than 6 months, V/Q SPECT leads to a 15% lower fetal dose and thus, is less hazardous. The fetal dose from CTPA increases with gestational age, while that from V/Q SPECT decreases. Furthermore, the maximum amount of fetal dose is received by fetal skeleton (i.e. on average about 1.8 and 3.9 times larger dose from SPECT and CT, respectively) Conclusions: V/Q SPECT should not always be preferred for pregnant patients suspected of PE. This finding is in contrast with the guidance to choose the preferred modality based on the maternal effective dose. The reason of this issue was discussed in this paper based on chord length distributions (CLD). The importance of considering fetal organs separately in MC calculations was also highlighted.

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