To explore the assessment methodology for internal dose to workers exposed to ¹³¹I radionuclide.

Workers were chosen in a ¹³¹I radiopharmaceutial manufacturer and a nuclear medicine department in a hospital using ¹³¹I to treat hyperthyroidism and thyroid cancer. A portable high purity germanium (HPGe) gamma spectrometer was used to measure the content of ¹³¹I in the thyroid for 4 consecutive times in a period of 7 d. The internal dose was estimated combining with the work rotation mode for workers dealing with ¹³¹I.

When the monitoring month was used as a typical month to estimate the internal dose, the annual committed effective dose was 0.09-1.93 mSv for the production staff engaged in the repackaging of ¹³¹I radiopharmaceuticals in the surveyed enterprise, and 0.06-0.58 mSv for the nuclear medicine staff in the surveyed hospital. After adjusting the monitoring result of the current monitoring period based on the rotation mode, the annual committed effective dose was estimated to be 0.06-1.22 mSv for radiopharmaceutical production workers and 0.03-0.15 mSv for nuclear medicine workers, respectively.

In the assessment of internal dose to radiation workers exposed to ¹³¹I, using a single time measurement result to estimate the annual dose would lead to a larger error. In the case of continuous monitoring, the result of subsequent monitoring periods should be corrected according to the result of previous monitoring periods. In order to accurately estimate the internal dose of workers exposed to ¹³¹I, it is necessary to take full account of the ¹³¹I exposure pattern, time and frequency and the internal contamination route. For workers who may be exposed to ¹³¹I with potential internal dose greater than 1 mSv/year, a 14 day-routine monitoring period was appropriate.

Internal exposure; Dose assessment; Nuclear medicine; ¹³¹I; Radiopharmaceutical production