Monte Carlo calculations of the radiation absorbed dose to a fetus of a pregnant patient from a dental bitewing X-ray exposure

In Sweden, the recommendation for intraoral X-ray exposure in dental radiology is that pregnant females should not use any extra protection than the mandatory thyroid lead collar. This recommendation is based on the knowledge that the dose to the fetus will be very low or negligible and therefore no extra protection is needed. However, we think it is important to test this recommendation using calculations based on the new International Commission on Radiological Protection (ICRP) phantoms for pregnant women. This project aims to do a Monte Carlo simulation of the absorbed dose distribution to a fetus at 25 weeks of pregnancy from a bitewing exposure, which is the most commonly used dental X-ray exposure. The project also aims to calculate the absorbed dose to organs and tissue in both the 25-week fetus and the pregnant mother. A lead collar, equivalent to 0. 25 mm lead, was created and added to the ICRP pregnant mesh phantom with a 25-week male fetus. A 60 kV bitewing exposure was simulated using MCNP6. 3. The radiation source was simulated using an RQR60 source and 10⁷ photons. The fetal organ absorbed doses are calculated for a bitewing exposure with a tube voltage of 60 kV and an exposure time of 0. 25 s for the phosphor plate receptor and 0. 05 s for the digital sensors. The fetal organs that received the highest absorbed dose for phosphor plate were the brain 27 nGy; red bone marrow, 25 nGy; and bone endosteum, 25 nGy. The simulations show that the absorbed dose to the 25-week fetus is significantly reduced due to absorption by the tissue of the mother. In general, the fetus receives an absorbed dose that is 0. 0015 of the mother's dose. For the 25-week fetus, the radiation exposure is low, and no extra protection is needed, e. g. covering the mother with a lead apron. These results could be of interest to the dentist, the physician, and the pregnant women before they agree to proceed with an intraoral dental exposure.