| Objective:⒈The goal of the study was to determine whether a 185MBq (5mCi) diagnostic dose of 131I produces a visually apparent stunning effect on the differentiated thyroid carcinoma patients postthyroidectomy who underwent 131I therapy. 2. Investigate quantitative indicator of diagnosis thyroid stunning.Methods: 1. 55 Patients with differentiated thyroid cancer, after thyroidectomy and 131I ablation therapy, received orally a 185MBq (5mCi) doses of 131I followed by a 48h diagnostic scan. The diagnostic scanning includes anterior whole-body images and spot anterior view of the neck and chest. The patients then underwent 131I ablation at a mean of 1.0days following the diagnostic dose. The range of 131I ablative dose was 3700MBq～9250MBq (100mCi～250mCi).A postablation scan was then obtained a mean 6.9days±1.1 after radioiodine ablation. The postablation scan includes anterior whole-body images and spot anterior view of the neck and chest. By comparing postablation scans with each patient's diagnostic scans to determine whether there is stunning phenomenon. Our observations were evaluated statistically using Fisher's exact test, rank sum test and t test. 2. Rectangular regions of interest (ROIS) were drawn around observable thyroid tissue in the neck and around an area in the neck devoid of 131I-concentrating tissues for background. Rx/Dx values were calculated and Receiver Operating Characteristic Curve (ROC) was drawn by SPSS software. The diagnostic threshold of Rx/Dx was formulated.Results: 1. 55 patients, 13 patients(23.64%)occurred stunning. 42 cases were not observed obvious stunning phenomenon. 2. Rx/Dx values<0.1455 can be defined as stunning.Conclusion: 1. Patients with differentiated thyroid cancer after thyroidectomy and 131I ablation therapy, follow-up process 185MBq (5mci) 131I diagnostic dose of whole body imaging can produce stunning effect. 2. Rx/Dx values can be used as one of the diagnostic reference for stunning.
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