CHARACTERIZATION OF TLD-100 DOSIMETER FOR MONITORING THE EXTREMITIES OF WORKERS IN NUCLEAR MEDICINE

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1 2011 International Nuclear Atlantic Conference - INAC 2011 Belo Horizonte,MG, Brazil, October 24-28, 2011 ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN ISBN: CHARACTERIZATION OF TLD-100 DOSIMETER FOR MONITORING THE EXTREMITIES OF WORKERS IN NUCLEAR MEDICINE Natalia C. E. S. Nascimento 1,2, Mércia L. Oliveira 2 and Êudice C. Vilela 2 1 Departamento de Energia Nuclear (DEN/UFPE) Av. Professor Luiz Freire, Recife, PE nataliafleming@hotmailcom 2 Centro Regional de Ciências Nucleares (CRCN-NE/CNEN) Av. Professor Luiz Freire, Recife, PE mercial@cnen.gov.br eudice@ig.com.br ABSTRACT Occupational exposure to ionizing radiation can occur due to various human activities, such as exposure during different stages of the nuclear fuel cycle, medical applications, research and all occupations that involve handling with radionuclides. This work aims to characterize extremity dosemeters based on LiF: Mg, Ti (TLD- 100) for use in nuclear medicine. For this, we used the dosimetric system EXT-RAD XD-100, associated with an the adjustable ring to the finger of workers. The dosimeters were irradiated on a PMMA phantom finger and standard radiation beams using a source of 137 Cs. The calibration of the dosimeters was carried in terms of Hp (0.07). In order to analyze the performance of the dosimetric system used, tests were made for the individual sensitivity, batch homogeneity, reproducibility, beta and photon energy response and angular response, according to the recommendations of the ISO The batch of dosimeters used in this study showed a value of homogeneity better than 6.9% and reproducibility better than 4.8%. The study of angular response of the dosimeters showed variation of the response less than 15%. The energy response test showed the variation of TL response below 50% in the energy range considered. Considering the results, we can conclude that the EXT- RAD dosimetric system meets the necessary requirements for application in extremity monitoring of individuals occupationally exposed in nuclear medicine. 1. INTRODUCTION Occupational exposure to ionizing radiation can occur as a result of various human activities, such as the different stages of the nuclear fuel cycle, medicine, research and all occupations that involve handling of materials with high concentrations of radionuclides. The increasing amount of applications using beta radiation sources and non-sealed sources requires the completion of a thorough dosimetric monitoring of workers exposed to these types of radiation [1]. This article will emphasize workers nuclear medicine. The medical staff in nuclear medicine gets radiation dose especially during multidose vials preparation kit, kit preparation of different radiopharmaceuticals, and the handling and administration to the patient [2].

2 These exposures occur principally in the fingers and hands, because these are body parts that are in direct contact or very close to the radiation source. For this reason it is important to monitor extremities of the body [3]. CNEN norms do not require workers to the use of dosimeters ends, only the use of wholebody dosimeters. Moreover, in Brazil there is no certification process for monitoring services in the extremities. However, there are labs that provide this type of monitoring, such as the Regional Center of Nuclear Sciences of the Northeast (CRCN-NE), the Institute of Radioprotection and Dosimetry (IRD) and the Center for Development of Nuclear Technology (CDTN), in addition to providing monitoring of the entire body [4]. Extremity dose assessment are usually carried out using thermoluminescence dosemeters (TLDs) because of their convenient size. For accurate measurement of Hp (0.07) the dosemeters must be physically thin to avoid significant attenuation of radiation. The dosemeters also needs to be robust because it may be placed on the hands carrying out manual work [2]. 2. MATERIALS AND METHODS The dosemeters tested uses a detector type TLD-100, thermally fixed to a polyamide band together with the bar code used for identifying the user. This band is inserted in a sealed case. This system is manufacturing by Harshaw/Bicron. The readers used for dosimetric analysis are both manufactured by Harshaw. We used the model 6600 (automatic reader) and 4500 (manual reader) We conducted the following characterization tests for these dosimeters: individual sensitivity, batch homogeneity, reproducibility, energy dependence and angular dependence. These tests were performed at the Division of Analytical and Nuclear (DITAN) Regional Center of Nuclear Sciences of the Northeast (NE-CRCN). After characterization, the dosimeters were calibrated and tests were performed in mixed fields. Such measurements were performed at the Laboratory for Calibration of Dosimeters (LCD) and the Laboratory of dosimeters (LDT) of the Center for Nuclear and Technological Development (CDTN). The result of the dosemeters is obtained in terms of Hp (0.07). That is personal dose equivalent at the depth of 0.07 mm according to the recommendations of ISO The dosimeters were irradiated in the sources of 137 Cs and 60 Co (gamma source) at 1 m distance and the source of 90 Sr/ 90 Y (beta source) to 20 cm. 3. RESULTS 3.1. Factor of individual sensitivity

3 To characterize the TL dosimetric system was necessary to determine the factor of individual sensitivity of TL detectors. Sensitivity factor of individual TL detectors were between 0.78 and There is no limit of acceptance for this test. 3.2Batch homogeneity Before carrying out performance tests, a group of 20 dosemeters was irradiated at a nominal dose value of 10 msv, and the evaluated value determined for the checking of the homogeneity of the dosemeter batch used. The variation coefficient obtained was 4.8%. It assures us the homogeneity of the batch being studied. The batch is considered homogeneous when the CV does not exceed 15% [5]. Table 1 - Results of the homogeneity test carried out in batch extremities monitors. Detectors Average (nc) s (%) CV H (%)

4 3.3 Reproducibility The system response reproducibility was obtained for a group of 10 dosemeters, irradiated at 10 msv, 10 times in a row, in the source 137 Cs. The study of reproducibility of the irradiation process was estimated considering the response of each group of reading. The values obtained do not exceed 6.9% difference between readings [5]. Table 2 - Results of the test reproducibility with the TL dosimeters. Detectors Average (nc) s (nc) CV R Angular dependence Figure 1 shows the average readings of the TL as a function of incidence angle of radiation. The results show that the different angles of incidence of the radiation beam in the dosimeters did not interfere significantly with the same response, because the variation of the response to the TL dosimetric system was less than 15%, remaining within acceptable limits required by ISO for this test [5].

5 Figure 1. TL response as a function of incidence angle of radiation. 3.5 Energy dependence In this work results were obtained in accordance with ISO standards (12794, 4037), for all values of Hp (0.07) used, and the recommendations of CASMIE, except for Hp (0.07) of 1 msv (Table 3), which showed a percentage change in the response in all considered energy range of 38.9%. This result can be attributed to greater uncertainty associated with this measure. It is noteworthy that the value of acceptance for this test adopted by CASMIE, refers only to the irradiation with photons and that in this work, the dosimeters were also irradiated with a beta source of 90 Sr/ 90 Y [5,6,7].

6 Table 3 - Energy dependence of TLD-100. Hp(0,07) (msv) Resposta percentual normalizada em relação ao Sr 90 +Y ,9% 3 28,7% 5 27,9% 7 29, ,1% 4. CONCLUSIONS It can be concluded that the dosimetric system XD EXT-RAD-100 meets the requirements for application in monitoring the extremities of individuals occupationally exposed to mixed beta-photon fields. The assessment of homogeneity did not exceed 6.9%. In relation to reproducibility values were obtained CV R less than 4.8%. To test the angular dependence of the dosimeters variation of TL response as a function of incidence angle of radiation was less than 15%. The test of energy dependence of the variation in responses to the 90 Sr+ 90 Y was less than 50%. ACKNOWLEDGMENTS The authors acknowledge the financial support provided by Capes and technical assistance from the laboratory CRCN and CDTN. REFERENCES 1. IAEA INTERNATIONAL ATOMIC ENERGY AGENCY. Assessment of occupational exposure due to external sources of radiation. Safety Guide. Vienna, 1999.

7 2. BERUS, D.; COBENS, P.; BUL, N. VAN DEN BROECK. Extremity doses of workers in nuclear medicine: mapping hand doses in function of manipulation. In: 11 th INTERNATIONAL CONGRESS OF THE INTERNATIONAL RADIATION PROTECTION ASSOCIATION (IRPA 11), May, 2004, Madrid. Spain, 2004 CD- ROM. 3. GARIN, E.; LAFFONT, S.; ROLLAND, Y.; OLIVIE, D.; LECLOIREC, J.; HERRY, J. Y.; BOUCHER, E; RAOUL, J. L.; BOURGUET, P. Safe radiation exposure of medical personnel by using simple methods of radioprotection while administering 131 I-lipiodo, therapy for hepatocellular carcinoma. Nuclear Medicine Communications, 24(6), , CNEN COMISSÃO NACIONAL DE ENERGIA NUCLEAR. CNEN-NN Diretrizes Básicas de Proteção Radiológica. D.O.U. Brasília, ISO - INTERNATIONAL ORGANIZATION FOR STANDARDIZATION. Nuclear energy Radiation protection Individual thermoluminescence dosemeters for extremities and eyes. ISO 12794, ISO - INTERNATIONAL ORGANIZATION FOR STANDARDIZATION. X and gamma reference radiation for calibrating dosemeters and dose rate meters and for determining their response as a function of photon energy. ISO , CASMIE, COMITÊ DE AVALIAÇÃO DE SERVIÇOS DE MONITORAÇÃO INDIVIDUAL EXTERNA, Desempenho de Sistemas de Monitoração Individual Critérios e Condições. Rio de Janeiro: Comissão Nacional de Energia Nuclear, Instituto de Radioproteção e Dosimetria, 1995.