BIOKINETIC MODEL DEVELOPMENT OF RADIOIODINE-131 VIA IN VIVO GAMMA CAMERA/8-SLICE CT TECHNIQUE: CASE-CONTROL STUDY OF FELINE HYPERTHYROIDISM

Abstract

Objectives: A biokinetic model of iodine in the thyroid was developed and applied to a case-control study of hyperthyroid cat undertaken the NaI-131 dose administration using a gamma camera/8-slice CT with the in vivo study. Methods: The case-control hyperthyroid cats were administered 55.5 or 3.7[Formula: see text]MBq of I-131 radioactive solution and continuously surveyed by a gamma camera. The scan schedule was preset as 5- or 10-min counting per each hour from the initial time to the sixth hour, then on the 24th, 48th and 72nd hours, respectively. An in-house developed program run in the MATLAB was applied to evaluate the biokinetic model of iodine in the thyroid, in compliance with the ICRP-30 report regulations. The model was defined by five compartments (namely: stomach, body fluid, thyroid, whole body, and excretion) and allowed one to simulate the variations of time-dependent I-131 radioactive concentration among various compartments of each study subject. The numerical simulation via MATLAB was compiled with the empirical evaluation to optimize the time-dependent concentration of I-131 within the above compartments. Results: The derived biological half-life values for stomach, body fluid, thyroid, whole body, and excretion, respectively, were as follows: 17, 3, 10, 5 and 140[Formula: see text]h for hyperthyroid cat, 18, 1, 8, 2, and 40[Formula: see text]h for control #1 cat, and 22, 2, 12, 4, and 20[Formula: see text]h for control #2 cat. The cumulative radioactive doses from both gamma-ray and beta particles were assessed via a simplified algorithm as 0.135, 0.0082, and 0.005 Gy, for hyperthyroid cat, control #1, and control #2 ones, respectively. Conclusion: The derived biokinetic model was found to be helpful in the evaluation of the metabolic mechanism in case of feline hyperthyroidism. The revealed deviations from available human biomodels can be used for refining the radioiodine treatment of pets with hyperthyroidism.