Fetal radiation dose from CT pulmonary angiography in late pregnancy: a phantom study

Pulmonary embolism (PE) is the leading direct cause of maternal mortality in the UK. Accurate diagnosis is important but, even though CT pulmonary angiography (CTPA) is the recommended imaging modality for PE in the general population, there is limited guidance for pregnant patients. Knowledge of the radiation doses to both the mother and the fetus is therefore important in the justification of CTPA in this situation. Dose measurements were made on three helical CT scanners, with an anthropomorphic phantom representing the chest and abdomen in late gestation. Estimated fetal doses from CT scans of the maternal chest were in the range of 60-230 microGy. Fetal dose reduction strategies (mA modulation, shielding with a lead coat, and a 5 cm shorter scan length) were investigated. These reduced the fetal dose by 10%, 35% and 56%, respectively. Fetal doses from a scan projection radiograph (SPR) of the maternal chest were insignificant when compared with the dose from a CT scan. However, if the SPR was not stopped before the "fetus" was directly irradiated, the dose measured on one scanner was 20 microGy.