Microscopic dose distributions due to iodine isotopes in thyroid

Area of Science:

• Nuclear Medicine
• Medical Physics
• Radiological Dosimetry

Background:

• Thyroid tissue contains colloid spheres, which can accumulate radioactive iodine isotopes.
• Accurate dosimetry is crucial for understanding radiation effects and optimizing treatments involving radioiodine.
• Microscopic dose distributions within these spheres are complex and require detailed calculation.

Purpose of the Study:

• To calculate microscopic electron dose distributions within thyroid colloid spheres containing various iodine isotopes.
• To assess the impact of sphere size and isotope energy on absorbed dose.
• To compute mean event-size distributions for 125I sources.

Main Methods:

• Utilized Berger's scaled absorbed dose functions and polynomial regression techniques.
• Calculated dose distributions for colloid spheres (15-150 micron radii) with uniformly distributed 123I, 125I, 131I, and 132I.
• Incorporated cross-follicular dose contributions for 131I, 123I, and 132I due to their higher electron/beta energies.

Main Results:

• Microscopic electron dose distributions were determined for specified thyroid tissue sphere sizes and iodine isotopes.
• The study quantified absorbed dose, considering self-dose and cross-dose contributions from adjacent follicles for higher-energy isotopes.
• Frequency and energy mean event-size distributions were computed for 125I disintegrations.

Conclusions:

• The applied methods provide a detailed understanding of microscopic radiation dose within thyroid tissue.
• Considering cross-follicular dose is important for accurate dosimetry of higher-energy beta-emitting iodine isotopes.
• This dosimetry data is essential for radioiodine therapy and thyroid cancer research.