Evaluation of maternal and fetal S-values from iodine isotopes in nuclear medicine using the Monte Carlo method

Internal dosimetry is critical in nuclear medicine, particularly for high-risk groups such as pregnant patients where minimizing radiation exposure to both the mother and fetus is essential. This study employs Monte Carlo simulations to calculate S-values for various target organs in a pregnant woman and her fetus, considering different maternal source organs and three iodine isotopes ( 131 I, 125 I, and 123 I). Our findings indicate that 131 I, with the highest emission energy, produces higher dose deposition in organs located farther from the source, while 125 I results in more localized dose absorption in adjacent tissues. The highest S-values for the mother were observed in the thyroid (5.8E-5 mGy/MBq·s for 123 I and 125 I) and the urinary bladder (3.7E-4 mGy/MBq·s for 131 I). In the fetus, the brain and skull received the highest radiation doses from 131 I, with values of 6.3E-6 and 5.6E-6 mGy/MBq·s, respectively. E-E-These results provide key quantitative insights for optimizing dosimetric protocols in clinical practice, aiding in the development of strategies to reduce radiation exposure in pregnant patients and their fetuses.