Correlation between external exposure and activity in patients undergoing 131I thyroid cancer therapy

Area of Science:

• Nuclear Medicine
• Radiological Physics
• Medical Dosimetry

Background:

• Iodine-131 (131I) is used in cancer therapy, necessitating accurate dosimetry for patient and public safety.
• Understanding 131I pharmacokinetics is essential for effective radiation protection protocols.

Purpose of the Study:

• To determine the uptake and clearance kinetics of 131I in inpatients undergoing cancer therapy.
• To correlate external dose measurements with internal 131I activity.
• To assess the temporal evolution of 131I activity in various body compartments.

Main Methods:

• Routine external dose survey measurements were employed to assess 131I activity.
• Bi-exponential models were used to describe iodine dynamics in the thyroid and the rest of the body.
• Effective retention constants and thyroid uptake percentages were calculated.

Main Results:

• A bi-exponential behavior characterized 131I uptake and clearance.
• External dose at 1 meter was correlated with thyroid remnant and body activity (average 52.8 ± 11.4 μSv GBq⁻¹ h⁻¹).
• Effective retention constants were determined for thyroid (0.23 ± 0.14 d⁻¹) and whole body (1.46 ± 0.34 d⁻¹), with thyroid uptake averaging 3.15 ± 3.36%.

Conclusions:

• The study provides quantitative data on 131I dynamics in cancer patients.
• Results are applicable to public and environmental radiation protection strategies.
• Accurate dosimetry aids in optimizing therapeutic doses and minimizing radiation exposure.