Biokinetic model of radioiodine I-131 in nine thyroid cancer patients subjected to in-vivo gamma camera scanning: A simplified five-compartmental model.

Chao-Chun Huang,Samrit Kittipayak,Lung-Kwang Pan,Yi-Shi Hwua,Shan-Ying Wang,Ya-Hui Lin,Juan Pardo-Montero

doi:10.1371/journal.pone.0232480

Abstract

A five-compartmental biokinetic model of I-131 radioiodine based on in-vivo gamma camera scanning results was developed and successfully applied to nine thyroid cancer patients who were administered 1,110 MBq I-131 in capsules for the residual thyroid gland ablation. The I-131 solution activity among internal organs was analyzed via the revised biokinetic model of iodine recommended by the ICRP-30 and -56 reports. Accordingly, a five-compartmental (stomach, body fluid, thyroid, whole body, and excretion) model was established to simulate the metabolic mechanism of I-131 in thyroid cancer patients, whereas the respective four simultaneous differential equations were solved via a self-developed program run in MATLAB. This made it possible to provide a close correlation between MATLAB simulation results and empirical data. The latter data were collected through in-vivo gamma camera scans of nine patients obtained after 1, 4, 24, 48, 72, and 168 hours after radioactive I-131 administration. The average biological half-life values for the stomach, body fluid, thyroid, and whole body of thyroid cancer patients under study were 0.54±0.32, 12.6±1.8, 42.8±5.1, and 12.6±1.8 h, respectively. The corresponding branching ratios I12, I23, I25, I34, I42, and I45 as denoted in the biokinetic model of iodine were 1.0, 0.21±0.14, 0.79±0.14, 1.0, 0.1, and 0.9, respectively. The average values of the AT dimensionless index used to verify the agreement between empirical and numerical simulation results were 0.056±0.017, 0.017±0.014, 0.044±0.023, and 0.045±0.009 for the stomach, thyroid, body fluid + whole body, and total, respectively. The results obtained were considered quite instrumental in the elucidation of metabolic mechanisms in the human body, particularly in thyroid cancer patients.

Highlights

This study is devoted to biokinetic model of radioiodine I-131 and its distribution in thyroid cancer patients using their in-vivo gamma camera scanning results
Noteworthy is that as early as in 1978, guidance in a comprehensive analysis of the radioiodine activity in various human organs was proposed by the ICRP-56 report [4], which introduced the main criteria for the iodine biokinetic model elaboration and linked its results with related data on healthy persons
The BKG values were subtracted from all net count rates at various ROIs, in order to eliminate the overcounting in the analysis

Summary

Introduction

This study is devoted to biokinetic model of radioiodine I-131 and its distribution in thyroid cancer patients using their in-vivo gamma camera scanning results. Noteworthy is that as early as in 1978, guidance in a comprehensive analysis of the radioiodine activity in various human organs was proposed by the ICRP-56 report [4], which introduced the main criteria for the iodine biokinetic model elaboration and linked its results with related data on healthy persons. The methodology of compiling the gamma camera technique with various theoretical biokinetic models became more straightforward and user-friendly after coupling the state-of-the-art gamma cameras with computed tomography (CT). This combination furnished more accurate identification of surveyed regions, i.e., borders of particular conventional compartments in patients’ bodies could be more readily distinguished

Methods

Results

Discussion

Conclusion