Internal exposure levels of thyroid ¹³¹I in nuclear medical staff

Background Based on numerous epidemiological studies, radionuclide ¹³¹I can result in thyroid disease.

Objective To study the contamination level of thyroid ¹³¹I in ¹³¹I treatment associated radiation workers in nuclear medicine departments in Shanghai.

Methods Based on a general survey on basic situation of nuclear medicine in Shanghai, the level of internal exposure of radiation workers involved in ¹³¹I treatment was assessed with questionnaires and on-site monitoring. A portable γ spectrometer was used for on-site detection, the intake and annual effective dose were estimated according to the measurement results. Physical examination reports were collected for radionuclide positive workers, and chromosome testing was performed.

Results  There were 579 nuclear medicine workers and 175 were engaged in ¹³¹I treatment in Shanghai. ¹³¹I was detected in thyroid of 18 workers, with a detection rate of 10.3%. Among them, the detection rates of thyroid ¹³¹I in nurses and cleaners were 23% and 25% respectively. The mean measured activity of thyroid ¹³¹I was 306.1 Bq and the maximum measured activity was 3716.9 Bq (nurse). The maximum intake was estimated at 37544 Bq and the median was 786.4 Bq. The average annual committed effective dose was 1.22 mSv and the maximum value was 14.87mSv. The chromosomal aberration rates of all detected workers were negative, and all blood indicators were normal except one with low hemoglobin.

Conclusion The annual dose of nuclear medical staff engaged in ¹³¹I treatment does not exceed the national standard limit, but the internal exposure of nurses and cleaners should not be ignored. On the basis of strengthening protection and decontamination, routine internal exposure monitoring should be carried out.