Assessing fetal radiation dose from iodine-125 seeds in pregnant breast cancer patients: an updated model.

Objective.The treatment of breast cancer during pregnancy requires careful consideration of consequences for both maternal and fetal health. In non-pregnant patients, the use of radioactive iodine-125 (¹²⁵I)-seeds is standard practice for localising non-palpable breast tumors before breast-conserving surgery. However, the use of¹²⁵I-seeds in pregnant patients has been avoided due to concerns about fetal radiation exposure.Approach.In this study a mathematical model was developed to estimate the fetal absorbed dose based on several factors: the radioactivity of the¹²⁵I-seed, the duration of implantation, and the distance between the¹²⁵I-seed and fetus as a function of maternal anatomy, gestational age, and fetal development. Three scenarios, representing a range of maternal and fetal anatomy, were evaluated, including a worst-case scenario from a radiation safety perspective.Main results.The results show that the fetal absorbed dose varies across the three scenarios, with ranges of 0.0-0.4 mGy, 0.0-1.0 mGy, and 0.0-1.6 mGy, depending on when the¹²⁵I-seed was implanted and when it was removed. These dose ranges are similar to conventional diagnostic x-ray scans. The maximum calculated absorbed dose (1.6 mGy) is unlikely to be reached in practice and is well below the 100 mGy threshold associated with possible fetal malformations. The associated theoretical cancer risk increase (0.016%) is minimal.Significance.The use of¹²⁵I-seeds as localisation method of breast tumors in pregnant patients results in low fetal radiation doses and should not be avoided due to dose concerns.