Letters to the Editor Stunning After Tracer Dosimetry TO THE EDITOR: We read with interest the article by Yeung

et al. (1) on therapeutic radioiodine uptake in thyroid remnants after tracer dosimetry. The authors reported decreased uptake in thyroid remnants if 131I-based dosimetry preceded therapy. Unlike other studies (2–5) in which a threshold of 111 MBq 131I was observed before thyroid stunning occurred, the authors reported decreased iodine uptake even with doses as low as 37 MBq 131I. We congratulate the authors on their excellent study. However, we cannot fully agree with their conclusion that the thyroid stun-ning was caused by radiation damage from the dosimetric tracer dose. Assuming the effect of thyroid stunning, one would expect a correlation between the amount of radioiodine in remnant tissue (diagnostic dose 3 diagnostic uptake) and the degree of stunning (ratio of diagnostic uptake to therapeutic uptake). This correlation cannot be found in the data presented in the study (r 5 20.08). With respect to this lack of correlation, we believe instead that there is considerable intratherapeutic stunning rather than dosimet-ric stunning. Within the first hours after therapeutic radioiodine administration, high radiation doses within thyroid remnant tissue can be expected to have major influence on the subsequent iodine clearance rate in the remnant tissue (iodine subsequently taken up in the stomach and radioiodine coming from the liver after de-iodination of radioactive thyroid hormones). This theory would also agree with the previous studies that reported a higher thresh-old for dosimetric doses