Evaluation of fetal dose during pelvimetry CT scan procedure by Monte Carlo using GATE

Pelvimetry is performed at the late pregnancy to measure the size of the pelvis through its different diameters in order to determine the possible modalities of delivery: by natural way or by programmed cesarean section. When a pregnant woman undergoes a radiological examination, the risk associated with radiation exposure is of concern. In general, the fetal dose cannot be measured directly, so Monte Carlo (MC) methods are used for this purpose. Therefore the objective of this study is to evaluate the fetal dose during a Computed Tomography (CT) pelvimetry examination by means of a MC method using Geant4 Application for Tomographic Emission code (GATE). A simulation of a CT pelvimetry examination was performed by modeling a Hitachi Supria 16-slice scanner that follows a CT pelvimetry protocol. A 16-diameter phantom is used to model the fetus inside a 32diameter phantom that represents the patient's body. The fetal dose in this simulation was 0.95 mGy. Other studies on fetal dose from pelvic CT scans found that it does not exceed a few mGys, which is not a real concern. On another hand, the dose showed a dependence on the variation of the tube current and also the voltage. Therefore, these parameters can be used as a basis for action to reduce exposure and limit risk during such examinations.