Abstract
Radioactive iodine is commonly used for the treatment of different thyroid conditions since the 1940s. The EANM has developed a standard pre-therapeutic procedure to estimate patient specific thyroid uptake at treatment of benign thyroid diseases. The procedure which models the time dependent fractional thyroid uptake is based on a two-compartment fitting system, one representing the thyroid and the other the blood. The absorbed dose is however only estimated for the thyroid and not for any other organ in the body. A more detailed biokinetic model for iodine is given by the ICRP and includes an iodide transport in the whole body. The ICRP model has 30 different compartments and 48 transfer coefficients to model the biokinetics of iodide and to model different transfer for inorganic iodide and organic iodine. The ICRP model is a recirculation iodine model, and the optimization is performed on the whole model and not exclusively on the thyroid as in the EANM procedure. Combining the EANM method and the ICRP model gives both patient specific estimations of thyroid uptake and retention and include most organs in the body. The new software gives both an improved patient specific dosimetry for the thyroid and an estimation of the absorbed dose to non-target organs and tissues like kidneys, urinary bladder, stomach wall, and uterus. Using the method described in this paper, the repercussions on the daily routines will be minimal.
Highlights
Radioactive iodine is commonly used for the treatment of benign thyroid diseases and of various forms of thyroid cancer since the 1940s [1,2,3,4]
In the transition to systemic biokinetic compartment modeling, the transfer of iodide in the whole human body is treated in the same way for both nuclear medicine [15] and occupational exposure [16] and based on the biokinetic models of Leggett [11, 12] to calculate the absorbed dose and the effective dose
For the 15 I-131 hyperthyroid patients, the mean timeintegrated activity coefficient (TIAC) for thyroid was estimated to 113 MBq h/MBq giving a female thyroid dose coefficient of 653 mGy/MBq
Summary
Radioactive iodine is commonly used for the treatment of benign thyroid diseases and of various forms of thyroid cancer since the 1940s [1,2,3,4]. This is due to the fact that iodine is an essential component in the production of the thyroid hormones thyroxine (T4) and triiodothyronine (T3), which regulate metabolic processes and are critical to growth and developments. The International Commission on Radiological Protection (ICRP) previously had two different biokinetic models for iodide, one for nuclear medicine [13] and another for occupational [14] exposure to estimate the distribution in different organs and tissues. In the transition to systemic biokinetic compartment modeling, the transfer of iodide in the whole human body is treated in the same way for both nuclear medicine [15] and occupational exposure [16] and based on the biokinetic models of Leggett [11, 12] to calculate the absorbed dose and the effective dose
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