Radioactive Seed Localization for the Resection of Nonpalpable Breast Lesions: A “No Later Than” Date Dosimetric Approach

Radioactive seed localization (RSL) using 125I is widely employed for the surgical resection of nonpalpable breast lesions due to its precision and scheduling flexibility. Although clinical experience supports its safety, quantifying radiation dose to surrounding healthy breast tissue remains important for establishing conservative operational guidelines, including acceptable implant duration prior to surgery. In this study, cumulative dose to healthy breast tissue from an implanted 125I localization seed was evaluated using two independent computational approaches: a simplified hemispherical breast model implemented in MATLAB and a Monte Carlo simulation developed in Mathematica. Both models incorporated dosimetric parameters from AAPM Task Group 43, including the dose-rate constant, radial dose function, and two-dimensional anisotropy function, along with tissue properties consistent with International Commission on Radiological Protection recommendations. Results from both models demonstrated that cumulative dose decreases rapidly with increasing distance from the seed and increases slowly with implantation time due to the low dose rate and long half-life of 125I. At a distance of 1 cm, cumulative dose reached approximately 3-4 cGy after 5 d and approximately 50 cGy only after extended implantation times exceeding 200 d. Agreement between the MATLAB and Monte Carlo models was within expected limits given differences in deterministic and stochastic modeling approaches. These findings indicate that radiation dose to healthy breast tissue from RSL remains well below thresholds associated with deterministic effects for clinically relevant implantation times. The results support the use of a conservative "no later than" removal date while reaffirming the radiological safety and practical advantages of 125I seed localization in breast cancer surgery.