engleski

Thyroid Stunning In-Vivo and In-Vitro

The aim of this work was to review recently published dosimetric data of in-vivo and in-vitro quantitative studies on thyroid stunning, in order to point out differences and try to formulate some recommendations for clinical situations. A non-linear regression analysis was applied to describe the extent of thyroid stunning as a function of the radiation absorbed dose of diagnostic radioiodine-131 (I-131) in thyroid cancer patients investigated by Jeevanram et al. (Nucl Med Biol, 1986) (1), Medvedec et al. (Eur J Nucl Med, 2001) (2) and Sinyuta et al. (Eur J Nucl Med, 2001) (3), as well as in patients who underwent two-step I-131 therapy for benign thyroid disease (Sabri et al., Eur J Nucl Med, 2001. The regression curves were fitted by using the mean values given for three (1, 2) and four (3) groups of patients and were compared with the models found recently in benign thyroid conditions (4) and in cultured thyroid epithelial cells after I-131 irradiation (Postgard et al., J Nucl Med, 2002) (5). According to the established analytical models, the threshold absorbed doses for the onset of thyroid stunning in-vivo were approximately 3 Gy and 30 Gy in malignant and benign conditions, respectively. Thyroid stunning amounted to roughly 50% in case of 3 Gy (5), 30 Gy (1, 2, 3) and 500 Gy (4) delivered to thyroid cells in in-vitro, malignant and benign conditions, respectively. It seems that a number of authors agree that there is hardly any scintigraphically relevant diagnostic amount of I-131 to be given prior I-131 therapy without thyroid stunning i.e. that is not recommended to deliver more than a few Gy into the target tissue in thyroid cancer patients. More investigations are required to confirm the applicability of the proposed in-vitro and benign in-vivo models in clinical situations but characteristic absorbed doses presented so far for in-vitro vs. in-vivo malignant vs. in-vivo benign thyroid environment differ roughly by a factor ten.

thyroid cancer; thyroid stunning; radioiodine therapy; dosimetry

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