Abstract: The aim of the present study was to evaluate the radiation doses received by medical staff during the emergency treatment of patients with recurrent papillary thyroid cancer received radioiodine (¹³¹I) radiotherapy, by using a real-time radiation monitoring system, for the purpose of radiation protection of occupational exposure. The patient was treated with radioiodine (¹³¹I ) for the second time and larynx edema occurred after treatment of ¹³¹I. There were three nurses and seven doctors participating in the emergency treatment of the patient and none of them wore a radiation dosimeter. In order to retrospectively assess the doses received by the medical staff, a new patient undergoing the same ¹³¹I radiotherapy was selected to simulate the radiation scenario of the original case. Real-time radiation monitoring system contained three personal dosimeters loaded with the function of delivering data by wireless to the repeater, where the signals were magnified and went through the radiation shielded wall of the ward to the hub, finally to the main unit of the system at the nurse station. One of the dosimeters was worn by the patient at the anatomic position of the sternal angle, the other two were laid at 20 cm (the bedside cupboard) and 150 cm away ( the wooden sill). Data of dose equivalent of the three dosimeters and corresponding accumulated dose equivalent were collected by the monitoring system. Data analyzing and graph making were performed with Microsoft Excel. The dose received by each medical staff was given by the sum of accumulated dose equivalent at different periods according to data at 20 cm or at 150 cm. The monitoring time was 86.4 hrs long after the patient was treated with ¹³¹I. Time -dose equivalent and -accumulated dose equivalent curves were made with average 6 000 data points for each curve. The fitting curves present exponential functions for time-dose equivalent courses, and logarithmic functions for time-accumulated dose equivalent courses. As a result, three nurses N1, N2, N3 received accumulated dose equivalent of 4 μSv, 7.5 μSv, and 4.8 μSv; and the seven doctors , D1, D2, D3, D4, D5, D6, D7, 8.2, 0.8, 1.5, 1.5, 1.5, 0.1 and 0.1 μSv, respectively. Among them, N1, N2, N3 and D1, staff of Department of Nuclear Medicine, were received relatively larger doses. The definitions and association of dose equivalent and effective dose were reviewed. The dose equivalent value at the 10 mm depth, H_p (10) could be considered a conservative or appropriate value for effective dose when the incident radiation present AP, LAT and ISO position to ICRU slab phantom, and the scatter radiation could contribute 2% dose equivalent to the 10mm deep site. Taking all together, under this case, we think even the doses received by medical staff were small compared to the dose limit for occupational exposure, however, personal dosimeter should be worn, and lead clothes should be prepared in the department of nuclear medicine, in order to implement the principle of as low as reasonably achievable (ALARA). This real-time monitoring system is proved to be necessary and effective tool for instant adjustment and optimization of the medical treatment procedures.

Key words: DTC, ¹³¹I radiotherapy, real-time radiation monitoring