A physiological systems model for iodine for use in radiation protection

Area of Science:

• Nuclear medicine
• Radiological protection
• Human physiology

Background:

• Existing biokinetic models for iodine are foundational for radiological dose assessments.
• Accurate modeling of iodine's systemic behavior is crucial for internal dosimetry.
• The International Commission on Radiological Protection (ICRP) provides current models for occupational exposure.

Purpose of the Study:

• To propose an updated biokinetic model for systemic iodine in the human body.
• To enhance dose assessments for internally deposited radioiodine.
• To consolidate and extend existing physiological models of the iodine cycle.

Main Methods:

• Summarized the biokinetic database for iodine in the human body.
• Developed a biokinetic model for systemic iodine, integrating circulating iodide, thyroidal iodine, and extrathyroidal organic iodine.
• Described thyroidal iodide uptake as a function of stable iodine intake and hormonal iodine secretion.
• Established baseline parameter values for reference adults.

Main Results:

• The proposed model predicts higher thyroid absorbed doses for very short-lived radioiodine isotopes compared to ICRP.
• Similar thyroid absorbed doses are predicted for iodine isotopes with half-lives of a few hours.
• Substantially higher absorbed doses to the stomach wall, salivary gland, and kidneys are estimated for most iodine isotopes.
• Dose estimates for radioiodine-labeled thyroid hormones differ significantly from current ICRP values.

Conclusions:

• The proposed systemic iodine biokinetic model offers improved accuracy for dose assessments.
• The model provides a more comprehensive understanding of radioiodine behavior in the human body.
• Findings suggest a need to re-evaluate current ICRP dose assessment methodologies for certain radioiodine scenarios.