Microdosimetrric analysis of 131I at in thyroid follicle

Background: Radionuclide iodine-131 is routinely used or proposed for diagnostic and therapeutic purposes. When radioiodine-labelled pharmaceuticals are administered to the body, radio iodide might be released into the circulation and taken up by the thyroid gland. The aim of this study accurate calculation of the absorbing dose of thyroid follicle cell nuclei for man, rat, mouse.Methods: Absorbing dose calculations were performed using the Monte Carlo code MCNPX 2.6.0 and energy imparted to the target volume with tally *F8 and nuclear decay data from ICRP 107.Results: The thyroid follicle were simulated according to real geometry. The model represents a single sphere-shaped thyroid follicle and consists of a spherical follicle lumen, a layer of follicle cells (shaped as a shell around the follicle lumen) and six spherical follicle cell nuclei distributed symmetrically at equal distances from the center of the follicle lumen. For the species-specific models, the follicle lumen diameter, follicle cell thickness and nucleus diameter are: (1) 50, 6 and 4 μm for mouse, (2) 70, 8 and 6 μm for rat and (3) 150, 10 and 8 μm for man, respectively. Calculations results represent when Volume of follicle cell nuclei increase, it absorbs less does.Conclusions: The results show that in the calculation of prescriptive dosage for treating hyperthyroidism and thyroid cancer, changes in absorbed dose in terms of thyroid volume (size) should be considered.

Keywords:

Absorbing dose , iodine-131 , thyroid follicle , mcnpx