Organ and fetal absorbed dose estimates from 99mTc-sulfur colloid lymphoscintigraphy and sentinel node localization in breast cancer patients.

UNLABELLED: The purpose of this retrospective study was to determine whether lymphoscintigraphy (LSG) for sentinel lymph node (SNL) mapping in a woman with a breast mass presents an unacceptable risk to her fetus. We assessed radiation-absorbed dose to various organs from 99mTc-sulfur colloid (TSC) LSG using standard internal absorbed dose assessment methodologies for both reference phantoms as well as for phantom models using the specific patient population characteristics such as total body and injected organ mass. The study also projected the radiation-absorbed dose to the fetus from LSG for SLN mapping.
METHODS: Data from 1,021 nonpregnant women with early-stage breast cancer who underwent SLN mapping and biopsy procedures were analyzed. Patients had a single-site intradermal injection of unfiltered TSC in 0.05 mL normal saline: 3.7 MBq (0.1 mCi) on the morning of surgery (1-d protocol) or 18.5 MBq (0.5 mCi) on the afternoon before surgery (2-d protocol). A standard internal dose calculation methodology was used to calculate absorbed doses to various organs and to a modeled fetus at 3-, 6-, and 9-mo gestation from the injection site as well as from systemic activity.
RESULTS: The highest estimated absorbed doses were observed for the reference 9-mo-pregnant model under the 2-d protocol. Absorbed doses of 14.9, 0.214, 0.062, 0.151, 0.004, 0.163, 0.075, and 0.014 mGy were received by the injected breast, heart, liver, lung, ovaries, thymus, total body, and fetus, respectively. Effective doses from the 2-d protocol were estimated to be 0.460, 0.186, and 0.245 mSv for the reference population, the total Memorial Sloan-Kettering Cancer Center (MSKCC) study patient population, and childbearing-age MSKCC patient population (i.e., <45 y old), respectively.
CONCLUSION: SLN procedures lead to a negligible dose to the fetus of 0.014 mGy or less. This is much less than the National Council on Radiation Protection and Measurements limit to a pregnant woman. Calculations using actual patient population characteristics resulted in lower organ dose estimates than more conservative reference models.