Abstract: Objective To investigate the feasibility of using thyroid 99mTcO4- imaging ROI ratio instead of 24 h radioactive iodine uptake (RAIU) for estimating 131I dose in individualized treatment of hyperthyroidism. Methods We retrospectively analyzed the clinical data of 132 patients receiving 131I treatment in our department between January and June, 2019. According to their 3 h/24 h RAIU peak ratio, the patients were divided into peak forward (≥80%) group and no peak forward (<80%) group. In the former group, the therapeutic 131I dose was calculated based the Marinelli formula (131I dose=thyroid mass×planned amount/24 h RAIU), and in the latter group, the correlation between the ROI ratio and the 24 h RAIU was analyzed, and the 131I dose was calculated using a modified Marinelli formula where 24 h RAIU was replaced by a converted ROI ratio. The two groups of patients were compared for antithyroid drug type and discontinuation time, thyroid hormones and related antibodies, thyroid area, thyroid mass and 131I dose. All the patients were and followed up for one year to analyze the treatment efficacy. The ROI ratios after the treatment were analyzed in the two groups using ROC curves. Results There was a significant positive correlation between the ROI ratio and 24 h RAUI in the no peak forward group (Y=58.13 + 0.2X, R2=0.118, P<0.05), and the formula for calculating 131I dose was converted into: 131I dose=thyroid mass× planned amount/(58.13+0.2×ROI ratio)%. Before the treatment, therapeutic 131I dose, thyroid hormone levels, TRAb, 3 h and 24 h RAIU, thyroid area, thyroid mass, and ROI ratio all differed significantly between the two groups (P<0.05). At 3 months after treatment, thyroid hormone levels, TRAb, TPOAb, thyroid area, thyroid mass, ROI ratio, response rate, hypothyroidism rate, cure rate, remission rate, and nonresponse rate were similar between two groups (P>0.05). At the 1-year follow-up, the composition ratios of hyperthyroidism, hypothyroidism and cured cases remained similar between two groups (P>0.05). ROC curve analysis showed that at 3 months after treatment, the optimal cutoff values of ROI ratio for predicting hyperthyroid recurrence and hypothyroidism were 15.79 and 6.33, respectively. Conclusion Thyroid 99mTcO4- imaging ROI ratio can be used for calculating 131I dose in individualized treatment of hyperthyroidism and for prognostic evaluation of the patients.

Key words: thyroid 99mTcO4- imaging; hyperthyroidism; 131I; region of interest; radioactive iodine uptake