Internal dosimetry estimates using voxelized reference phantoms for thyroid agents

Area of Science:

• Medical Physics
• Radiological Dosimetry
• Nuclear Medicine

Background:

• Internal dosimetry is essential for evaluating radiation risks from radiopharmaceuticals used in diagnosing thyroid disorders.
• Current methods may not fully capture organ dose distributions, especially with varying radiopharmaceutical uptake and administration techniques.

Purpose of the Study:

• To estimate organ doses for diagnostic procedures involving Iodine-131, Iodine-123, and Technetium-99m.
• To compare dose calculations using ICRP voxel phantoms versus stylized phantoms.
• To investigate the impact of thyroid uptake and administration methods on organ doses.

Main Methods:

• Utilized the Monte Carlo transport method with International Commission on Radiological Protection (ICRP) reference voxel phantoms.
• Calculated organ doses directly, bypassing traditional S values and Source-Anything Factors (SAFs).
• Computed chord length distributions (CLDs) for gender-based comparisons.

Main Results:

• Standard S values are insufficient for accurate organ dose calculation for Iodine-123 and Technetium-99m.
• Increased thyroid uptake significantly elevates doses to the thyroid and adjacent organs.
• Voxel phantoms yield higher organ dose estimates than stylized phantoms, particularly between 5-55% uptake.

Conclusions:

• Direct Monte Carlo calculations with voxel phantoms provide more accurate internal dosimetry for thyroid diagnostics.
• Stylized phantom models may underestimate organ doses, potentially affecting risk assessments.
• Administration techniques and varying radiopharmaceutical uptake necessitate detailed, individualized dosimetry.