Background The development of medical technology has given rise to the use of radionuclides, especially 18F, 99mTc, and 131I, in medical diagnosis and therapies. It is necessary to implement regular internal exposure monitoring for the medical staff who are occupationally exposed to radionuclides.
Objective This study aims to measure the individual doses in 21 nuclear medicine personnel exposed to radionuclides 131I, 99mTc, and 18F from three sizable Class-A tertiary hospitals in Nanjing, and to estimate the intake and committed effective dose of those with higher-than-detectionlimit 131I exposure.
Methods The gamma spectrum from neck to hip was collected with high purity germanium detector, and the single measurement was used for two analyses. Firstly, two efficiency curves for thyroid and whole body were graduated respectively using standard sources. After data collection, the efficiency curve of thyroid was used to calculate 131I dose, and the whole-body efficiency curve was used to calculate 99mTc dose and 18F dose. The calculation results were used to derive 14-day intake by long-term intake model; the 14-day intake was used to calculate 14-day committed effective dose and annual committed effective dose under the premise of a representative measurement.
Results There were 9 nuclear medicine staff reporting occupational exposure to 131I, and 5 of them were detected 131I positive. There were 9 staff reporting occupational exposure to 99mTc, and 1 of them were detected 99mTc positive. There were 16 staff applying 18F, and all of them were detected 18F positive. Of the 5 staff whose 131I exposure levels were higher than detection limit, the highest 14-day committed effective dose was 0.92 mSv, the average 14-day committed effective dose was 0.27 mSv, and the annual average committed effective dose was 7.0mSv with a peak value of 24 mSv.
Conclusion The investigation results show that the annual average committed effective dose of the positive exposed staff is higher than the limit of 1 mSv, indicating that they are required to implement radiation internal exposure monitoring. Even taking into account the positive exposure rate, internal exposure makes considerable contribution to annual committed effective dose. The highest estimate exceeds the limit of 5-year average of committed effective dose. Therefore, the radiation internal exposure monitoring for the nuclear medicine staff exposed to radionuclide 131I is a task brooking no delay.
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