Study On The Radiation Dose Of Staff And The Radiation Level Of Environment At ¹³¹I Treatment Site In A Hospital

Objective:To understand the radiation of ¹³¹I in treatment site of a hospital.To discuss the occupational exposure of the staff in this site.To estimate the risk of radiation-induced cancer of the staff in this site.Methods:1.A total of 25 patients with thyroid cancer were administrated ¹³¹I at a total dose of 82880 MBq.After administration,the ambient dose equivalent rate of the ward was detected with X-andγ-ray detectors;At the time of injection,the ambient dose equivalent rate of the injection room was detected with X-andγ-ray detectors;After patients discharge,surface contamination of the ward was detected withα/βsurface contamination meter;During patients hospitalization and on the day of discharge,air samples were collected from ¹³¹I treatment site and office area.The air samples were measured using HPGeγ-ray spectrometer and the concentration of ¹³¹I in air was calculated.2.A total of 21 patients with thyroid cancer were administrated ¹³¹I at a total dose of 68820 MBq.Staff of thyroid ¹³¹I activity was measured by portable grammar spectrometer.After data processing,the thyroid ¹³¹I activity were knew.Then ¹³¹I intake and effective dose were estimated.Air samples were collected from ¹³¹I treatment site and office area.Based on the detection results of ¹³¹I concentration in the air and the working conditions of the on-site investigation,the annual intake of ¹³¹I and the effective dose to be accumulated in this site were estimated.3.The external exposure of staff was estimated based on the results of ambient dose equivalent rate and personal dose monitoring from the on-site investigation.The risk of radiation-induced cancer was estimated by the total effective dose of the staff and nominal risk coefficient.Results:1.The ambient dose equivalent rate for the outdoor protective walls,hall-way protective walls,protective doors and upstairs floors of the ¹³¹I treatment ward were0.24～0.48μSv/h,0.22～1.44μSv/h,0.15～0.55μSv/h and 0.14～0.16μSv/h,respectively.The ambient dose equivalent rate around the nurse’s eye lens,abdomen,and hand position when the patients were first injected after administration were0.42～0.71μSv/h,0.26～0.41μSv/h and 8.09～25.3μSv/h,respectively.2.The mean surface contamination of toilet,toilet floor,sink,ward floor,table top,bed surface（head）,bed surface（middle）and bed surface（foot）in ¹³¹I treatment wards before cleaning were 26.8～73.0 Bq/cm~2,0.54～20.7 Bq/cm~2,1.00～12.4 Bq/cm~2,1.18～17.4 Bq/cm~2,0.42～2.02 Bq/cm~2,0.23～8.72 Bq/cm~2,0.27～3.91 Bq/cm~2and0.18～1.26 Bq/cm~2,respectively.After staff cleaning,the mean surface contamination of all locations in the ward decreased compared with that before cleaning,and the decrease rate were 86.7%,16.5%,44.6%,2.7%,8.3%,38.2%,25.4%,20.8%,respectively.Surface contamination of ¹³¹I treatment area（except ward）and office area were 0.07～5.15 Bq/cm~2and 0.04～0.85 Bq/cm~2,respectively.3.Within 4h after administration,the ¹³¹I air concentration in the corridor of the¹³¹I treatment site and the office area were 1.74 Bq/m~3and 0.66 Bq/m~3,respectively.The ventilation air flow rate in the ¹³¹I treatment was 0.50 m/s.Ventilation decreased the concentration of ¹³¹I in air by 29.7%,79.7%and 53.3%compared with the previous day during hospitalization and on the day of discharge.The concentration of¹³¹I in the air of nurse station and injection room were 0.05～0.27 Bq/m~3and 0.09～0.50Bq/m~3,respectively.The concentration of ¹³¹I in the air of the treatment site and office area was 0.04～3.58 Bq/m~3.4.¹³¹I thyroid activity of doctors,nurses and cleaners in the ¹³¹I treatment site were 435.08～814.64 Bq,1056.06～1151.60 Bq and 508.67～919.21 Bq,respectively.The annual effective dose of doctors,nurses and cleaners were estimated to be2.32～4.34 m Sv/a,5.63～6.14 m Sv/a and 1.81～3.28 m Sv/a,respectively,by personal monitoring in vitro.The effective dose for doctors,nurses and cleaners were 0.08m Sv/a,0.10 m Sv/a and 0.05 m Sv/a,respectively,by air personal monitoring.The annual effective dose of nurse’s the lens,abdomen and hands were 0.03 m Sv/a,0.02m Sv/a and 1.21 m Sv/a,respectively.Individual monitoring results for doctors,nurses and cleaners in the ¹³¹I treatment site were 0.13～0.31 m Sv/a,0.23～2.35 m Sv/a and1.73 m Sv/a,respectively.5.The total effective dose of doctors,nurses and cleaners in the ¹³¹I treatment site were 2.45 m Sv/a,6.06 m Sv/a and 3.54 m Sv/a,respectively.The percentage increase in lifetime risk of cancer after 30 years 0.30%,0.75%,0.44%,respectively.Conclusions:1.In this hospital the radiation of external exposure of ¹³¹I treatment site is low and the shielding is effective.2.Before ward cleaning,the surface contamination is lower than the standard limit except for the toilet in this hospital.The surface contamination of ¹³¹I treatment ward is reduced after cleaning,but the cleaning effect is different for different locations and different cleaning methods.3.There is ¹³¹I of the air at this site in this hospital.The nurses’station and injection room are located at the intersection of the two areas and have a higher air¹³¹I concentration than the rest of the office area.Ventilation is the primary way to reduce the concentration of ¹³¹I in the air and thought ventilation can further reduce the concentration of ¹³¹I in the air.4.The external exposure dose of cleaner is higher than that of other staff,so it is necessary to pay attention to the training of radiation protection knowledge of cleaner in daily work,improve their awareness of protection,so as to reduce their occupational external exposure dose.5.The internal exposure dose of nurse is higher than that of other staff,so attention should be paid to the concentration of ¹³¹I in the ambient air of nurses,and ventilation should be strengthened to further reduce their occupational internal exposure dose.6.The internal radiation doses of the staff of this hospital are all higher than 1m Sv by personal monitoring in vitro.And it accounted for a relatively high proportion of the annual effective dose.Therefore,individual internal radiation doses of the staff in the ¹³¹I treatment site should be monitored of the internal radiation doses according to the actual situation.7.In this experiment,the results of estimating internal radiation dose by in vitro direct measurement method and air sampling method are quite different,and the influencing factors need to be further studied.8.Staff of the ¹³¹I treatment site in this hospital,whose lifetime risk of cancer has increased as a result of occupational exposure.To further reduce staff risk of occupational radiation disease by regularly changing their work area or reducing their workload.