Fetal Dose Variations in Lung Scintigraphy of Pregnant Woman: The Role of Fetal Body Habitus

This study aims to address the radiation exposure incurred by lung scintigraphy in pregnant patients suspected of pulmonary embolism and to investigate the dose variations due to different body habitus of the fetus.
In this respect, seven computational models of pregnant women and fetus in three trimesters of pregnancy were used and Monte Carlo calculations were performed using Monte Carlo n-particle –extended (MCNPX) code version 2.6.0 to assess absorbed dose coefficients. Time-integrated activities for three radiopharmaceuticals considered in this study were also extracted from the available reference biokinetic data.
Fetal dose coefficients (mGy/MBq) for three radiopharmaceuticals labeled with 99mTc were estimated for reference pregnant phantoms at three trimesters of gestation and 10th, and 90th fetal growth percentiles were also considered during the last two trimesters. The results show that the fetal dose coefficients were 2.09 × 10-2, 5.71 × 10-3, and 4.44 × 10-3 mGy/MBq for 99mTc MAA, 8.31 × 10-4, 8.68 × 10-4, and 1.27 × 10-3 mGy/MBq for 99mTc Technegas, and 7.85 × 10-3, 2.42 × 10-3, and 2.66 × 10-3 mGy/MBq for 99mTc DTPA aerosol, respectively. According to the results the factor of fetal body habitus adds variation to the fetal dose within ±15%.
Considering one of the uncertainty components of fetal dose, that is the fetal body habitus, the dose variations were well below the safety threshold for the fetus (the threshold from ICRP Publication 84 for fetal cancer risk). Therefore, to check the safety of the diagnostic examination in terms of radiation dose to the fetus, it is sufficient to take into account the reference dose values in clinical practice.