Study On Occupational Internal Exposure Of Nuclear Medicine Workers

BackgroundNuclear medicine is one of the fastest developing fields in radiology.Occupational exposure of nuclear medicine staff is characterized by the operation of non-sealed source.They not only receive external radiation,but also receive internal radiation due to the intake of radionuclides.At present,the monitoring of nuclear medicine staff in China is limited to external radiation.Their per capita annual dose is higher than other radiation workers.The work and literature of nuclear medicine occupational exposure in China are mainly focused on the evaluation of construction project,workplace protection and surface pollution monitoring,internal radiation monitoring method and internal radiation dose are rarely reported.International attention is paid to the internal exposure of nuclear medicine workers.In the disease of diagnosis and treatment in nuclear medicine department,99mTc,131I and 18F are used more frequently than other nuclides.The usage amount of 131I is maximum and131I is volatile.If improper operation protection measures are adopted,it is easy to cause serious air pollution in the workplace,and cause the workers to be exposed.The internal monitoring of nuclear medicine workers,especially the monitoring of 131I,needs attention.ObjectiveTo establish the determination method of internal monitoring of nuclear medicine workers in ChinaTo establish the rapid direct measurement method of 131I in the thyroid of nuclear medicine workers,To estimate the internal radiation dose of nuclear medicine workers.Methods1.According to the principles and methods of the IAEA safety guidelines,combined with the specific situation of actual operation of nuclear medicine in China,the questionnaire is designed to determine the necessity of internal monitoring of nuclear medicine workers.Select the nuclear medicine workers to test the questionnaire.2.Combined with the instrument and equipment conditions of major radiation health technology institutions,choose the more simple and applicable equipment,establish the organ counting measurement method,select large general hospital and specialist hospital for actual monitoring of nuclear medicine workers,and verify the feasibility of the method.3.In order to interpret the source of pollution within the wokers,large flow air sampling and individual sampling are adopted in the selected hospitals for monitoring and analysis of the distribution of radioactive 131? aerosols in the air.4.Calculate the annual intake and committed effective dose according to the results of thyroid direct measurement and air sampling.Results1.The necessity of internal monitoring of 89 staff of 7 hospitals in 5 provinces was conducted.Seven parameters including workload,operation type and protection conditions of 89 workers were investigated,and the determination method of the necessity of nuclear medicine internal monitoring was obtained by calculation.The results showed that the decision coefficient range of 89 staff members was from 0.3 to 99.5,the mean D value was 22.44,and the median was 6.4.97.8%of investigated nuclear medicine workers were determined to be necessary to receive internal monitoring.The analysis showed that the d values between different hospitals and different occupational groups(doctors,technicians and nurses)were significantly different(F = 17.39,P<0.001).The order of d value was the nurses>technicians>doctors.d values of the nurses were the largest,indicating that the risk of internal exposure of nurses was the biggest,and the risk of internal exposure of doctors was the smallest.2.The direct measurement method of thyroid was established.The Nal portable gamma spectrometer was used,and the measurement time was 120 seconds.When collimator was used and not used,the calibration coefficient was 0.0094 cps/Bq and 0.0152cps/Bq,the minimum detection activity(MDA)was 19 Bq and 23Bq,respectively.A total of 97 workers in 2 general hospitals and 1 cancer hospital were measured directly.131? was detected in the thyroid of 31(32.0%of 97 workers)workes,the activity range was from 25.11 Bq to 1980.30Bq,the mean value was 415.71 Bq,and the median value was 192.43 Bq.The positive rate of thyroid monitoring in different occupational groups was different,but not statistically significant(?2=3.45,P>0.05).3.The results of ? surface contamination level in the workplace of nuclear medicine department were from 0.08 Bq/cm2 to 38 Bq/cm,and the range of external exposure level was from 0.08 ?Sv/h to 760?gSv/h.The pollution of 131? in the air of nuclear medicine department with 131? treatment was widespread.The concentration range of 131? in the air in three hospitals was from 0.58 Bq/m3 to 11251.88 Bq/m3.In the air sampling at the same location,the results of the individual sampler were higher than that of the large flow sampler.The concentration of 131? in the air increased with the number of patients and the total dose.4.Under the condition of conventional monitoring cycle of 7 days,14 days and 30 days,the maximum value of committed effective dose caused by 131? intake in a year was 11.00 mSv?7.36 mSv and 7.47mSv,respectively.The calculated dj of workers responsible for 131? automatic subpackage and the estimated internal radiation dose based on direct measurement of thyroid had shown good consistency.5.The comprehensive analysis found that the positive rate of thyroid monitoring may be different because the work load and protection measures were different in different hospitals.The average activity of 131? in thyroid positive workers was different.The hospital with the highest positive rate of thyroid monitoring had the highest average of 131? activity in the thyroid positive workers.Conclusion1.The questionnaire and decision method of the necessity of internal monitoring of nuclear medicine workers based on seven parameters such as operation type,work load and protection measures were established.2.The method of direct measurement of 131I count in thyroid by NaI portable gamma spectrometer was established,and the calculated dj of workers responsible for 131I automatic subpackage and the estimated internal radiation dose based on direct measurement of thyroid have shown good consistency.3.The pollution of 131I in the air of nuclear medicine department with 131I treatment was widespread.The internal pollution was not only limited to workers operating 131Idirectly.The internal dose of some nuclear medicine workers was significant.The prevention and treatmeCt of 131I pollution in the air of nuclear medicine department need to be strengthened.