%0 Journal Article %A Charlotta Lundh %A Ulrika Lindencrona %A Per PostgƄrd %A Therese Carlsson %A Mikael Nilsson %A Eva Forssell-Aronsson %T Radiation-Induced Thyroid Stunning: Differential Effects of 123I, 131I, 99mTc, and 211At on Iodide Transport and NIS mRNA Expression in Cultured Thyroid Cells %D 2009 %R 10.2967/jnumed.108.061150 %J Journal of Nuclear Medicine %P 1161-1167 %V 50 %N 7 %X Recent clinical and experimental data demonstrate that thyroid stunning is caused by previous irradiation and may influence the efficacy of 131I radiation therapy of thyroid cancer and possibly hyperthyroidism. To avoid stunning, many clinics have exchanged 131I for 123I for pretherapeutic diagnostic imaging and dose planning. Furthermore, recent in vitro studies indicate that 131I irradiation reduces iodide uptake by downregulating the expression of the sodium iodide symporter (NIS). The rationale for this study was therefore to study effects on iodide transport and NIS messenger RNA (mRNA) expression in thyrocytes exposed to both 123I and 131I in addition to some other potentially interesting radionuclides. Methods: Thyrotropin-stimulated thyroid cell monolayers were exposed to 0.5 Gy of 123I, 131I, 99mTc, or 211At, all being radionuclides transported via NIS, in the culture medium for 6 h, or to various absorbed doses of 123I or 131I for 48 h. NIS mRNA expression was analyzed using quantitative reverse-transcriptase polymerase chain reaction. Results: Iodide transport and NIS mRNA expression were reduced by all radionuclides. At the same absorbed dose, iodide transport was reduced the most by 211At, followed by 123I and 99mTc (equally potent), whereas 131I was least effective. The onset of NIS downregulation was rapid (<1 d after irradiation) in cells exposed to 123I or 211At and was delayed in cells irradiated with 131I or 99mTc. Iodide transport and NIS expression were recovered only for 211At. 123I reduced the iodine transport and the NIS mRNA expression more efficiently than did 131I at an equivalent absorbed dose, with a relative biological effectiveness of about 5. Conclusion: The stunning effect per unit absorbed dose is more severe for 123I than for 131I. Despite the lower absorbed dose per unit activity for 123I than for 131I, stunning by 123I cannot be excluded in patients. The degree to which iodide transport capacity and NIS mRNA expression are reduced seems to be related to the biological effectiveness of the type of radiation delivering the absorbed dose to the target, with 211At (which has the highest relative biological effectiveness) causing the highest degree of stunning per unit absorbed dose in the present study. %U https://jnm.snmjournals.org/content/jnumed/50/7/1161.full.pdf