Evaluation of radiation dose to working staff with draw out 18F –FDG in cyclotron center

• Main Authors: Ming-Jay Kuo, 郭明杰
• Other Authors: Jao-Perng Lin
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/2zu68c

碩士 === 元培科學技術學院 === 影像醫學研究所 === 94 === Medical advances in positron emission tomography (PET) have developed rapidly, as evidenced by ten medical cyclotrons that currently produce PET radiation pharmaceuticals in Taiwan. Staff employees are unfortunately exposed to the highest radiation dose in the manufacturing of radiation pharmaceuticals. This study evaluates radiation dose exposure towards laboratory technicians as a function of the cyclotron measurement device used when drawing out 18F fluorodeoxyglucose ( 18F –FDG) that occurs during processing and transporting if radiation pharmaceuticals. The dose of radiation exposure having accumulated in the technologists is evaluated. To determine the exposure rate, the study measured (detection levels OR a detector) containing thermoluminescent dosimeter (TLD)TLD-700 and neutron rem detector (NRD). TLD-700 were attached at various parts of the body not only to determine the dose of radiation exposure found in a technologist, but also to evaluate the radiation risk exposure to sensitive organs that could be received when drawing out of 18F –FDG studied. The gamma dose distribution was acquired by the 3-plane placements of the TLD-700 in the space of cyclotron room and transporting the radiation pharmaceuticals (including automobiles and PIG) and the extrapolation code. The NRD measured the cyclotron room to obtain the neutron dose distribution. Those results were compared to the recommendations of the International Commission on Radiological Protection (ICRP) report publication 60. Experimental results indicated that while drawing out 18F –FDG (1500 mCi 40 min weekly) for a year (50 weeks), the hands of a technologist received the highest dose, with an average of the right finger 355.88 mSv y-1 and left finger 267.59 mSv y-1. Additionally, the average equivalent doses with protection to the right eye and left were 17.11 mSv y-1 and 15.10 mSv y-1, respectively. The average whole body effective dose with protection was estimated at 8.05 mSv y-1. While the radiation pharmaceuticals were transported, the PIG (tungsten shield 2.25 cm) carried 100 mCi radiation pharmaceuticals to determine the accumulated 1-hour exposure rate and to evaluate the PIG surface dose. According to those results, at the horizontal plan of height of 20 centimeters, the maximum and mean photon absorption rates are 2000~3000 μGy h-1 at the shielding surface, and at the position of 20 centimeters away from shielding surface, the radiation is reduced 400 μGy h-1. At the same condition, the PIG was placed in a car (lead shield 2 cm) to determine the accumulated 1-hour exposure rate to evaluate the car surface dose. At the horizontal plan of height of 50 centimeters, the maximum and mean photon absorption rates are30 μGy h-1 at the shielding surface. Devices used include operating the cyclotron for 60 minutes and 35 μA for the beam current, in which the gamma and neutron radiation distribution in a cyclotron room were estimated. Experimental results indicated that, at the cyclotron body front, the maximum and mean photon absorption rates are12~20 Gy h-1 at the shielding surface; at the cyclotron body lateral or posterior shielding surface, those absorption rates are 6~10 Gy h-1. During distribution of neutron radiation, the target side (cyclotron right side), maximum and mean exposure rates are 20~25 Gy h-1 at the shielding surface; the other sides are under 10 Gy h-1. However, their exposure dose did not exceed the limits regulated by law. In conclusion, reducing excessive radiation exposure to workers by minimizing the time spent in close contact with the radiation pharmaceuticals, increasing the distance from the source and providing suitable protective shielding devices are the most effective approaches to ensure workplace safety. Key Words: Cyclotron, Thermoluminescent dosimeter, Equivalent dose, Effective dose