Monitoring of external irradiation and superficial contamination in a conventional PET / Cyclotron center

Full text: The use of Positron Emission Tomography is increasing not only as a diagnostic and research practice in Nuclear Medicine, but also as a complementary tool in 3D Radiotherapy planning. The production and use of FluoroDeoxiGlucose, (18F-FDG) involves a sequence of procedures during which all staff are exposed. In our conventional PET center, technologists, radio chemists and physicists are involved in the so-called 'Cyclotron and Production Line of Radioisotopes for PET'. For that reason, it is essential to carry out a whole-body and extremities individual dosimetry monitoring and a permanent working areas control. A procedure for external exposure rate and external contamination measurements have been established in our department, as a part of the quality control in Radiation Protection aspects for the production line of FDG. The values of ambient dose equivalent rate were measured with a Geiger Mueller detector, and the superficial contamination measurements are made with an indirect method (sweep test). The monitoring was made in six areas of the PET/cyclotron installation. These areas are the cyclotron bunker, Fluor-Deoxi-Glucose quality control laboratory, a bio-sterilized area where the synthesis process is done, fractioning room, uptake room and scanner room. Cyclotron and quality control laboratory areas: The mean ambient dose equivalent rate at 1m from the cyclotron bunker during the isotopes production, has values of 0.6 + 0,2μSv/h and this is the mean value of ambient dose equivalent rate, which is consider as background of the installation. To make the quality control in the laboratory, a sample of 200 microlitres of FDG is taken to analyze the radiochemical purity and pyrogens detection. In this laboratory the millipore filter integrity is also checked with the bubble test. The mean ambient dose equivalent rate in contact with the 5 cm thick Pb shielding at chest level , with the sample and the filter inside the shielding was 0,7 + 0,3 μSv/h. The monitoring of the waste disposal after the quality control was 0.5 + 0,2 μSv/h and the highest value of external contamination registered was 85 + 20 μSv/h in the bubble test peak. Fractioning room: during the fractioning, the values are, at eyes level 0,313 + 0,1 mSv/h, thorax 3,58 + 1,5 μSv/h, gonads 1.9 + 1,8 μSv/h. These values depends on the performance of the module synthesis (50-70%),without considering the radioisotope decay. Uptake room: injecting 0.185 GBq (5 mCi) average of 18F-FDG per patient, yielded 2,9 + 0,8 μSv/h at 2m from the patient after injection. Scanner room: 81 + 28μSv/h, this measurement is the highest value registered in this room at 0,30 m from patient thorax when the scanning is beginning. Image acquisition console 0,66 + 0,1 μSv/h during the scanning at 4m from the patient. Conclusions: based on the measurements obtained in this type of facility in accordance with the monitoring plan over seven years of operation, we have seen that in normal working conditions, the annual effective doses registered with our individual dosimetry system with TLD, was well within dose constraint limits for Nuclear Medicine workers, 6mSv/year (Class II). The measured dose was even lower for people who work in the part of the installation categorized as Class I. Considering that this center type has an extra equipment like a particle accelerator, laboratory and radiopharmacy, it has the advantage that positron emitters have shorter half-life than those used in conventional nuclear medicine, although they have higher energy. The reason for which there are lower doses, alludes to the fact that the work is made by established procedures (Class I), the continuous installation improvements and the implementation of redundant safety systems that intended to decrease the probabilities of abnormal situations. (author)