Abstract: In order to optimize the protective measures for patients with differentiated thyroid carcinoma (DTC) after iodine-131 therapy, the variation of dose equivalent rate to hands and necks of the patients was monitored at short distance. 100 DTC patients were divided into two groups with 50 cases in each group. Group 1 was thyroid remnant ¹³¹I ablation therapy group (dose from 3 700 to 4 440 MBq), and Group 2 with ¹³¹I treatment for recurrent and metastatic lesions (dose from 6 660 to 8 140 MBq). To determine dose equivalent rate to hands and necks, an Inspector Alert gamma detector was used to measure the dose rate on discharge,and at one week,two weeks,one month and two months after discharge. The detector was placed 30 cm away from the necks and palms, and closely contacted skin, respectively. The results showed that: (1) All the measured dose rates were high at the time of discharge after iodine-131 therapy, and the dose rates gradually decreased over time. The dose equivalent rates measured 30 cm away from the necks and palms one month after discharge and all the results for two months after discharge were lower than 0.25 μSv/h. (2) At the time of discharge, average dose equivalent rates to the necks were higher than those to the hands(p＜0.05), while at the time of one week, two weeks, one month after discharge (p＜0.05), the average dose equivalent rates to the hands were higher than those to the necks. (3) Dose equivalent rates for Group 1 in front of the neck at the time of discharge and at one week, two weeks, one month after discharge were higher than the results of Group 2(p＜0.05), while dose equivalent rates for Group 2 measured by closely contacting the hands were lower than those for Group 1 at the same time (p＜0.05). As all the results for the DTC patients measured at the time of discharge were higher than 20 μSv/h, we recommend that the patients should avoid intimate contact with others within a week after discharge and also avoid long-time contacts within two weeks after discharge. The DTC patients can have normal social activities with other people around one month after a large doses of ¹³¹I therapy, but in accordance with the principle of optimization of radiation protection, they should avoid intimate contact with vulnerable groups (such as infants, young children and pregnant women, etc.). Two months after therapy, as dose equivalent rates would have dropped to the background level, there is no need to take any radiological protection measures. As dose equivalent dose rates to the hands could be high due to contamination, patients particularly with the second course of treatment should take radiological protection measures.

Key words: differentiated thyroid carcinoma, dose equivalent rate, iodine-131