Determining the Fetal Dose in Ventilation/Perfusion Scan Using Monte Carlo Simulation

Pulmonary embolism (PE) is a blockage in one of the pulmonary arteries. Ventilation/Perfusion (V/Q) scan is one the diagnostic methods of PE in pregnant women. It is necessary to investigate fetal dose and compare it with recommended values. The aim of this study was to determine the fetal dose in V/Q scan using Monte Carlo simulation. An adult pregnant woman phantom and all her displaced organs were used for simulation. Source organs were defined for each of the radiopharmaceuticals used in two lung ventilation and perfusion scans, including lung and bladder for 133Xe, 81mKr, and technetium diethylene-triamine-pentaacetate aerosol (99mTc-DTPA-aerosol) for lung ventilation scan, and lung, bladder, and liver for 99mTc-technetium macroaggregated albumin (MAA) for lung perfusion scan. Fetal dose was determined and evaluated using the simulation output after calculations. For 99mTc-MAA at prescription dose of 200 MBq, fetal dose was found to be 1.01 mGy, maximum fetal dose was 1.97 mGy, and both of them were more than the values recommended by International Commission on Radiological Protection (ICRP). For 99mTc-DTPA, fetal and maximum doses were below 1 mGy, and for 133Xe and 81mKr, fetal dose was negligible. It is concluded that considering higher dose to the fetus (200 MBq of 99mTc-MAA), if the pregnant woman scan is needed, her awareness must be done.