METHODOLOGY AT CIEMAT WHOLE BODY COUNTER FOR IN VIVO MONITORING OF RADIOIODINE IN THE THYROID OF EXPOSED POPULATION IN CASE OF NUCLEAR EMERGENCY

METHODOLOGY AT CIEMAT WHOLE BODY COUNTER FOR IN VIVO MONITORING OF RADIOIODINE IN THE THYROID OF... Abstract Iodine-131 is one of the main concerns from the point of view of radiological protection in a short term after a nuclear accident. The WBC Laboratory of CIEMAT has developed a methodology for in vivo monitoring of radioiodine in the thyroid of exposed individuals in case of emergency. Thyroid–neck phantoms of different sizes are required for calibrating the detection systems in appropriate counting geometries for the measurement of exposed population. A Low-Energy Germanium (LEGe) detector and a Fastscan Counter were calibrated using a set of thyroid phantoms fabricated by CIEMAT. Each neck phantom consists of a Lucite cylinder with a vial source of 131I. Counting efficiencies depending on age and thyroid sizes were obtained to be used to determine the activity of 131I in internally contaminated people. DL of 131I varies with the age, being in the range of 5–8 Bq for the LEGe detector and 26–42 Bq for the Fastscan. Detection of intakes resulting in Committed Effective doses far below 1 mSv are guaranteed for thyroid monitoring in a few days after the accidental exposure assuming a scenario of acute inhalation or ingestion of 131I by members of the public. INTRODUCTION In case of a nuclear accident large amounts of radioiodine may be released to the environment with the subsequent risk of contamination of the population. The thyroid gland is the target organ where de iodine is retained during few weeks after the intake took place. In vivo measurements of 131I in thyroid by gamma spectrometry are recommended to quickly identify the most contaminated people in an emergency scenario. The determination of the retained activity in the thyroid and the result internal dose estimate, help to decide about taking appropriate counter measures to avoid or minimize undesirable health effects due to the ionizing radiations. Germanium or NaI(Tl) detectors are commonly used for in vivo monitoring of exposed individuals at risk of incorporation of gamma emitters into the body. Radioactive sources of known activity in anthropomorphic phantoms simulating neck and contaminated thyroid gland of the individuals are required for calibration purposes. Lawrence Livermore National Laboratory (LLNL, USA) in collaboration with the European Radiation Dosimetry Group (EURADOS) organized in 2016 an international intercomparison on measurement and dose estimates of radioiodine deposited in the thyroid, using several (separate) sources of 131I and 125I in vials which were introduced in a ANSI neck phantom(1). In vivo counting facilities have developed calibration and measurement procedures for monitoring workers but a gap was identified after Fukushima NPP accident regarding available calibration protocols for children(2). The use of different phantoms simulating neck and thyroid of members of different groups of age are crucial for a proper calibration and accurate determination of the 131I activity in thyroid, in order to estimate reliable internal doses. The main goal of this work is to describe a methodology developed at CIEMAT Whole Body Counter (WBC) for the calibration and in vivo monitoring of 131I in the thyroid of contaminated adults and children. Thyroid phantoms of different sizes simulating children and adults were fabricated by CIEMAT following ICRP 89 recommendations(3). MATERIALS AND METHODS Detection systems CIEMAT Whole Body Counting facility counts with a Low-Energy Germanium (LEGe) detector system and a Fastscan (NaI(Tl)) Counter for in-vivo measurement of 131I in thyroid. The active area of each LEGe detector is 3800 mm2, with a diameter of 70 mm and a thickness of 25 mm, with a Carbon Epoxy window, 0.5 mm thick(4). The LEGe detectors are placed inside a shielded room of 13 cm steel walls lined with Pb, Cd and Cu with independent ventilation to reduce environmental background. LEGe detectors present an excellent resolution and good efficiency at low and moderate energies (10–1000 keV). One of the four LEGe is used for thyroid monitoring at a distance of 15 cm from the neck and for a counting time of 20 min (Figure 1). Figure 1. View largeDownload slide Thyroid monitoring using a LEGe detector inside a shielded room at CIEMAT WBC. Figure 1. View largeDownload slide Thyroid monitoring using a LEGe detector inside a shielded room at CIEMAT WBC. The Fastscan Counter was manufactured by Canberra Industries. It includes two large sodium iodine detectors (NaI(Tl)) of 7.6 cm × 12.7 cm × 40.6 cm along the vertical axis(5). The Fastscan whole body counter is designed to quickly and accurately monitor people for internal contamination of gamma-emitting radionuclides with energies between 100 keV and 2 MeV (Figure 2). Figure 2. View largeDownload slide Fastscan counter. Figure 2. View largeDownload slide Fastscan counter. Both systems are operating using Genie2000 Gamma Spectrometry software(6) which provides a complete set of operating procedures to perform calibration functions, to analyze subjects and for quality assurance operations. Design of the thyroid–neck phantom set A ‘family’ of neck–thyroid calibration phantoms for children (Figure 3) was fabricated at CIEMAT (Spain). Each phantom consists of a Lucite cylinder with a lateral cavity where the thyroid gland simulator is introduced. Each cylinder size was designed according to the age of the individual following ICRP 89 recommendations(3). The contaminated thyroid gland is simulated using a cylindrical vial filled with a homogeneously distributed liquid solution of 131I. The selected volumes of the different thyroid glands are 1.8, 3.4, 7.7, 12 ml, which correspond to 1, 5, 10, 15-year-old children, respectively. Adult neck–thyroid phantom was designed according to ANSI 13.44(7) standard with a thyroid gland volume of 20 ml simulating reference male and 17 ml for reference female. Figure 3. View largeDownload slide CIEMAT neck–thyroid phantom set. Figure 3. View largeDownload slide CIEMAT neck–thyroid phantom set. The neck perimeters of the different phantoms were calculated based on anatomical measurements to different ages of children. The neck thickness of the phantoms was calculated from measurements of CT studies (Table 1). Table 1. Neck phantom sizes for different ages. Age (y) Perimeter (cm) Height (cm) 1 22 ± 2 7,1 ± 0,6 5 26 ± 3 8,2 ± 0,9 10 30 ± 4 10 ± 1 15 34 ± 5 11 ± 2 Age (y) Perimeter (cm) Height (cm) 1 22 ± 2 7,1 ± 0,6 5 26 ± 3 8,2 ± 0,9 10 30 ± 4 10 ± 1 15 34 ± 5 11 ± 2 Table 1. Neck phantom sizes for different ages. Age (y) Perimeter (cm) Height (cm) 1 22 ± 2 7,1 ± 0,6 5 26 ± 3 8,2 ± 0,9 10 30 ± 4 10 ± 1 15 34 ± 5 11 ± 2 Age (y) Perimeter (cm) Height (cm) 1 22 ± 2 7,1 ± 0,6 5 26 ± 3 8,2 ± 0,9 10 30 ± 4 10 ± 1 15 34 ± 5 11 ± 2 RESULTS AND DISCUSSION Efficiency calibration for different counting geometries of in vivo measurement of 131I in the thyroid (children and adults) were performed at the WBC of CIEMAT using Fastscan Counter and LEGe detector system. Fastscan Counter is used for a rapid measurement of thyroid activity in exposed individuals in case of radiological or nuclear emergency due to its excellent efficiency at medium and high energies. LEGe detectors are more suitable in case of complex cases of internal contamination due to their high resolution especially in a range of 10–1000 keV. Calibration sources In both detection systems (LEGe and Fastscan), efficiency calibration curves (counts/gamma) versus energy (keV) were obtained using 131I as calibration source for 1, 5, 10 and 15-year-old children and for the reference female. A mock-iodine of 133Ba and 137Cs was formerly used for the reference male calibration. All sources were manufactured and certificated by Laboratory of Ionizing Radiation Metrology (LMRI-CIEMAT) (Table 2). Table 2. Activities of the calibration sources. Date of certificate Age (y) A (kBq) ΔA (kBq), k = 2 10/07/2015 1 29,46 0,59 10/07/2015 5 29,79 0,6 10/07/2015 10 59,5 1,2 10/07/2015 15 49,9 1,0 31/10/2014 Woman 40.6 1,2 (2.8%) 10/07/2015 Man 18,81 0,38 Date of certificate Age (y) A (kBq) ΔA (kBq), k = 2 10/07/2015 1 29,46 0,59 10/07/2015 5 29,79 0,6 10/07/2015 10 59,5 1,2 10/07/2015 15 49,9 1,0 31/10/2014 Woman 40.6 1,2 (2.8%) 10/07/2015 Man 18,81 0,38 Table 2. Activities of the calibration sources. Date of certificate Age (y) A (kBq) ΔA (kBq), k = 2 10/07/2015 1 29,46 0,59 10/07/2015 5 29,79 0,6 10/07/2015 10 59,5 1,2 10/07/2015 15 49,9 1,0 31/10/2014 Woman 40.6 1,2 (2.8%) 10/07/2015 Man 18,81 0,38 Date of certificate Age (y) A (kBq) ΔA (kBq), k = 2 10/07/2015 1 29,46 0,59 10/07/2015 5 29,79 0,6 10/07/2015 10 59,5 1,2 10/07/2015 15 49,9 1,0 31/10/2014 Woman 40.6 1,2 (2.8%) 10/07/2015 Man 18,81 0,38 Calibration of LEGe detector for measurement of 131I in thyroid of adults and children An individual detector (Det 1) of the LEGe detection system placed inside the shielded room and positioned at a detector-thyroid distance of 15 cm was calibrated by both thyroid–neck phantom and radioactive sources simulating contaminated thyroid gland for each children and adults geometry performed(8). Figure 4 shows the counting efficiency (cps/γ) versus energy (keV) curves for the different counting geometries implemented. Figure 4. View largeDownload slide Counting geometry for thyroid calibration and counting efficiency versus energy for CIEMAT LEGe detector. Figure 4. View largeDownload slide Counting geometry for thyroid calibration and counting efficiency versus energy for CIEMAT LEGe detector. The efficiency value corresponding to the main emission of 131I (364 keV) is utilized in order to calculate activity in a possible intake. Table 3 shows the efficiency values for different sizes of thyroid glands. Table 3. Efficiency in LEGe detector for 364 keV. V (ml) Eff (cps/γ) 364 keV Δeff (cps/γ) 1,80 0,002375 5,14E-05 3,4 0,002411 4,88E-05 7,7 0,002310 4,62E-05 12 0,001981 6,70E-05 17 0,001970 9,93E-05 20 0,002801 9,93E-05 V (ml) Eff (cps/γ) 364 keV Δeff (cps/γ) 1,80 0,002375 5,14E-05 3,4 0,002411 4,88E-05 7,7 0,002310 4,62E-05 12 0,001981 6,70E-05 17 0,001970 9,93E-05 20 0,002801 9,93E-05 Table 3. Efficiency in LEGe detector for 364 keV. V (ml) Eff (cps/γ) 364 keV Δeff (cps/γ) 1,80 0,002375 5,14E-05 3,4 0,002411 4,88E-05 7,7 0,002310 4,62E-05 12 0,001981 6,70E-05 17 0,001970 9,93E-05 20 0,002801 9,93E-05 V (ml) Eff (cps/γ) 364 keV Δeff (cps/γ) 1,80 0,002375 5,14E-05 3,4 0,002411 4,88E-05 7,7 0,002310 4,62E-05 12 0,001981 6,70E-05 17 0,001970 9,93E-05 20 0,002801 9,93E-05 Calibrations of Fastscan Counter for the in vivo measurement of 131I in thyroid (adults and children) The calibration of Fastscan was carried out for standing up counting geometry(9). The neck–detector distance is 12 cm. The height to the thyroid depends on the age of individuals (Table 4) according to WHO and ANSI 13.30. Table 4. Source volume (ml) and ground-thyroid distance of the thyroid, CIEMAT Fastscan calibration. V (ml) Age (y) h (cm) 1,8 1 61,5 3,4 5 92,0 7,7 10 117,0 12 15 girl 138,5 12 15 boy 143,5 17 Woman 139,0 20 Man 156,5 V (ml) Age (y) h (cm) 1,8 1 61,5 3,4 5 92,0 7,7 10 117,0 12 15 girl 138,5 12 15 boy 143,5 17 Woman 139,0 20 Man 156,5 Table 4. Source volume (ml) and ground-thyroid distance of the thyroid, CIEMAT Fastscan calibration. V (ml) Age (y) h (cm) 1,8 1 61,5 3,4 5 92,0 7,7 10 117,0 12 15 girl 138,5 12 15 boy 143,5 17 Woman 139,0 20 Man 156,5 V (ml) Age (y) h (cm) 1,8 1 61,5 3,4 5 92,0 7,7 10 117,0 12 15 girl 138,5 12 15 boy 143,5 17 Woman 139,0 20 Man 156,5 Upper detector was calibrated for children aged 1 and 5 years, and upper detector for the rest of the set phantoms (Figure 5). Figure 5. View largeDownload slide Counting geometry for thyroid calibration and counting efficiency versus energy for CIEMAT Fastscan Counter. Figure 5. View largeDownload slide Counting geometry for thyroid calibration and counting efficiency versus energy for CIEMAT Fastscan Counter. The maximum of efficiency curves corresponds to the energy around 400 keV, close to the main emission of 131I (364 keV), which is noted in Table 5. Table 5. Efficiency in Fastscan superior detector in 364 keV. V (ml) Eff (cps/γ) 364 keV Δeff (cps/γ) 1,8 0,022834 8,81E-04 3,4 0,036963 1,41E-03 7,7 0,035254 1,48E-03 12 0,032312 1,19E-03 12 0,034102 2,10E-03 17 0,028840 1,69E-03 20 0,028798 1,69E-03 V (ml) Eff (cps/γ) 364 keV Δeff (cps/γ) 1,8 0,022834 8,81E-04 3,4 0,036963 1,41E-03 7,7 0,035254 1,48E-03 12 0,032312 1,19E-03 12 0,034102 2,10E-03 17 0,028840 1,69E-03 20 0,028798 1,69E-03 Table 5. Efficiency in Fastscan superior detector in 364 keV. V (ml) Eff (cps/γ) 364 keV Δeff (cps/γ) 1,8 0,022834 8,81E-04 3,4 0,036963 1,41E-03 7,7 0,035254 1,48E-03 12 0,032312 1,19E-03 12 0,034102 2,10E-03 17 0,028840 1,69E-03 20 0,028798 1,69E-03 V (ml) Eff (cps/γ) 364 keV Δeff (cps/γ) 1,8 0,022834 8,81E-04 3,4 0,036963 1,41E-03 7,7 0,035254 1,48E-03 12 0,032312 1,19E-03 12 0,034102 2,10E-03 17 0,028840 1,69E-03 20 0,028798 1,69E-03 Validation of the 131I monitoring calibration for adults and children The validation of the thyroid calibration was carried out using the same thyroid phantom set and vials but with different radionuclides. Liquid sources of 133Ba (90%) and 137Cs (10%) were used for the simulation of 131I emissions. Table 6 summarizes the activities and Type A uncertainties (Δ) of the different mocks used. Each vial was introduced in the corresponding neck phantom, placed at the same conditions of the calibration geometry. Five measurements were performed for each phantom representing 1, 5, 10 and 15-year-old children, reference male and female adults. Table 6. Activities of the mock sources with 133Ba and 137Cs. V (ml) 133Ba A (Bq) 133Ba ΔA (Bq) 137Cs A (Bq) 137Cs ΔA (Bq) 1,83 9458,8 14,8 942,11 2,89 3,43 9454,3 14,8 941,67 2,89 7,63 9493,6 14,9 945,58 2,90 12,03 9531,3 14,9 949,33 2,91 17,03 9488,7 14,9 945,09 2,90 V (ml) 133Ba A (Bq) 133Ba ΔA (Bq) 137Cs A (Bq) 137Cs ΔA (Bq) 1,83 9458,8 14,8 942,11 2,89 3,43 9454,3 14,8 941,67 2,89 7,63 9493,6 14,9 945,58 2,90 12,03 9531,3 14,9 949,33 2,91 17,03 9488,7 14,9 945,09 2,90 Table 6. Activities of the mock sources with 133Ba and 137Cs. V (ml) 133Ba A (Bq) 133Ba ΔA (Bq) 137Cs A (Bq) 137Cs ΔA (Bq) 1,83 9458,8 14,8 942,11 2,89 3,43 9454,3 14,8 941,67 2,89 7,63 9493,6 14,9 945,58 2,90 12,03 9531,3 14,9 949,33 2,91 17,03 9488,7 14,9 945,09 2,90 V (ml) 133Ba A (Bq) 133Ba ΔA (Bq) 137Cs A (Bq) 137Cs ΔA (Bq) 1,83 9458,8 14,8 942,11 2,89 3,43 9454,3 14,8 941,67 2,89 7,63 9493,6 14,9 945,58 2,90 12,03 9531,3 14,9 949,33 2,91 17,03 9488,7 14,9 945,09 2,90 A proficiency test was carried out in order to evaluate ‘Relative Bias’ and ‘Repeatability’ parameters according to ISO/IEC 28 218 Standard(10). Results for both detection systems (LEGe and Fastscan) were in compliance with acceptance criteria of ISO 28 218 parameters, relative bias (Br) is between [−0.25, 0.5] and repeatability (SBr) is <0.4. Sensitivity of the detection systems for thyroid monitoring. Detection limit According to ISO/IEC 28 218(10) the value of the detection limit (DL) indicates the ability of the in vivo laboratory to detect a radionuclide incorporated by an individual and deposited in total body or in organs. The DL is mainly dependent on the person (tissue thickness attenuation), the measurement geometry, the efficiency and counting time. DL can be calculated from the measurement of a blank person or a blank phantom (Figure 6) as follows: LD=2k1−α(1t·ε)2(p2mn0+(p2m)2n0)+k21−α(1t·ε)1−k21−α(u(ε)(ε))2 where n0 = # counts in the Surface B1 and B2; p = # channels of the neck; m = # channels in the Surface B1 and B2; ε = efficiency; u(ε) = efficiency uncertainty; and k1−α = 1.645. Figure 6. View largeDownload slide Detection limit (DL). Figure 6. View largeDownload slide Detection limit (DL). In both (LEGe and Fastscan) detection systems DL was calculated by each counting geometry using neck phantom and blank thyroid gland in routine measurement conditions (Tables 7 and 8). Table 7. Detection limits of 131I in thyroid for different configurations of LEGe detector. DL Detector 1 LEGe, t = 1200 s, d = 15 cm Age (y) 1 5 10 15 Woman Man DL (Bq) 6,1 4,6 5,3 6,2 7,9 6,4 DL Detector 1 LEGe, t = 1200 s, d = 15 cm Age (y) 1 5 10 15 Woman Man DL (Bq) 6,1 4,6 5,3 6,2 7,9 6,4 Table 7. Detection limits of 131I in thyroid for different configurations of LEGe detector. DL Detector 1 LEGe, t = 1200 s, d = 15 cm Age (y) 1 5 10 15 Woman Man DL (Bq) 6,1 4,6 5,3 6,2 7,9 6,4 DL Detector 1 LEGe, t = 1200 s, d = 15 cm Age (y) 1 5 10 15 Woman Man DL (Bq) 6,1 4,6 5,3 6,2 7,9 6,4 Table 8. Detection limits of 131I in thyroid for different configurations of Fastscan Counter. DL Fastscan, t = 300 s, d = 12 cm Age (y) 1 5 10 15 girla 15 boya Woman Man DL (Bq) 41,9 26,1 25,6 27,8 36,2 31,7 33,8 DL Fastscan, t = 300 s, d = 12 cm Age (y) 1 5 10 15 girla 15 boya Woman Man DL (Bq) 41,9 26,1 25,6 27,8 36,2 31,7 33,8 aThey are the same phantom and their heights of measurement in the Fastscan are different, which are referenced in Table 4. Table 8. Detection limits of 131I in thyroid for different configurations of Fastscan Counter. DL Fastscan, t = 300 s, d = 12 cm Age (y) 1 5 10 15 girla 15 boya Woman Man DL (Bq) 41,9 26,1 25,6 27,8 36,2 31,7 33,8 DL Fastscan, t = 300 s, d = 12 cm Age (y) 1 5 10 15 girla 15 boya Woman Man DL (Bq) 41,9 26,1 25,6 27,8 36,2 31,7 33,8 aThey are the same phantom and their heights of measurement in the Fastscan are different, which are referenced in Table 4. Estimation of committed doses for the exposed population in emergency scenarios Committed effective dose for children (E(70)) and adults (E(50)) have been estimated taking into account the values of DL (Bq) for 131I that were obtained for both detection systems (LEGe and Fastscan) for the different counting geometries implemented. The scenarios of internal exposure considered are acute inhalation of 131I type F and acute ingestion. Measurements are supposed to be performed three days after intake. Activity detected is assumed to be the same as the DL (Bq) for 131I and the committed effective dose was estimated. The results confirm that three days after the intake, the in vivo measurement of 131I in thyroid for the exposed population applying the methodology developed by CIEMAT WBC allows estimating doses about tens of microSievert for a short counting time of 300 s. CONCLUSIONS CIEMAT Whole Body Counting Laboratory has developed a calibration methodology for the in vivo measurement of 131I in the thyroid of exposed population (adults and children). A Fastscan Counter and a LEGe detector inside a shielded room are used for this purpose. A set of neck phantoms for thyroid calibration were manufactured at CIEMAT using Lucite with density and attenuation similar to soft tissue, on the basis of ICRP 89 and ANSI 13.44 recommendations for 1, 5, 10 and 15 years old children and adult male and female. Iodine-131 was used as calibration source. Calibration efficiency values depend mainly on the source volume, neck phantom–detector distance, relative detector-source position and attenuation due to neck thickness. Counting efficiency using Fastscan (5 min as counting time) is greater than the one for LEGe detector (20 min) for the same configuration. LEGe detector is suitable in case of complex internal contamination due to the excellent resolution of this equipment allowing the correct identification and quantification of different isotopes emitting similar gamma emissions. CIEMAT WBC has validated this in vivo method for thyroid monitoring which can be applied in case of radiological or nuclear emergency involving accidental intake of 131I through inhalation or ingestion by workers and members of the public of different ages. DL varies with the age of individuals, being in the range of 5–8 Bq of 131I for the LEGe detector and 26–42 Bq for the Fastscan Counter. Detection of intakes resulting in committed effective doses far below 1 mSv are guaranteed for thyroid monitoring in a few days after the accidental exposure assuming an scenario of acute inhalation or ingestion of 131I by members of the public. CIEMAT WBC has participated in the 2016 EURADOS/LLNL intercomparison of thyroid monitoring and dose evaluation to validate new ANSI thyroid phantom(11) and is currently involved in the Cathymara project ‘Child and Adult Thyroid Monitoring After Reactor Accident’ (OPERRA, 7FP EURATOM, 2016–17). ACKNOWLEDGEMENT Eduardo Garcia Toraño and Virginia Peyres from Metrology Laboratory, Inmaculada Sierra and Carolina Hernandez from In vitro Bioassay Laboratory and Infrastructure Division of CIEMAT for their contribution in the fabrication of the thyroid–neck phantom set and the preparation of radioactive sources. REFERENCES 1 Hickman , D. P. et al. . Thyroid phantom measurements in Joint EURADOS-LLNL intercomparison exercise . Radiat. Prot. Dosim. 178 ( 2 ), 152 – 159 ( 2018 ). Google Scholar CrossRef Search ADS 2 Lopez , M. A. et al. . Lessons learned from the EURADOS survey on individual monitoring data and internal dose assessments of foreigners exposed in Japan following the Fukushima Daiichi NPP accident . Radiat. Prot. Dosim. 170 ( 1–4 ), 402 – 406 ( 2016 ). Google Scholar CrossRef Search ADS 3 ICRP . Basic anatomical and physiological data for use in radiological protection reference values. ICRP Publication 89 . Ann. ICRP 32 ( 3–4 ), 225 – 227 ( 2002 ). 4 López Ponte , M. A. and Bravo , T. N. A Low Energy Germanium Detector System for lung counting at the WBC facility of CIEMAT . Radiat. Prot. Dosim. 89 ( 3–4 ), 221 – 227 ( 2000 ). Google Scholar CrossRef Search ADS 5 Canberra . Manual Fastscan Counter ( 2004 ). 6 Canberra . Manual Genie/Abacos 2000 ( 1999 ). 7 American National Standards Institute . I., ANSI/HPS N13.44–2014. Thyroid Phantom Used in Occupational Monitoring ( 2014 ). 8 Pérez López , B. and Navarro Amaro , J. F. Determinación in-vivo de I-131 en tiroides mediante el sistema LEGe Detector 1., CIEMAT/DR/DPI/08/13, Editor. 2013 , CIEMAT. 9 Pérez López , B. and Navarro Amaro , J. F. Determinación in-vivo de I-131 en tiroides mediante los sistemas NaI(Tl) y Fastscan, CIEMAT/DR/DPI/07/13, Editor. 2013 , CIEMAT. 10 ISO . ISO 28218: Radiation protection—performance criteria for radiobioassay, ISO, Editor. 2010 . p. 45. 11 Etherington , G. et al. . CAThyMARA report: technical guidelines for radioiodine in thyroid monitoring. OPERRA Deliverable D5.31 ( 2017 ). © The Author(s) 2018. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Radiation Protection Dosimetry Oxford University Press

METHODOLOGY AT CIEMAT WHOLE BODY COUNTER FOR IN VIVO MONITORING OF RADIOIODINE IN THE THYROID OF EXPOSED POPULATION IN CASE OF NUCLEAR EMERGENCY

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Abstract

Abstract Iodine-131 is one of the main concerns from the point of view of radiological protection in a short term after a nuclear accident. The WBC Laboratory of CIEMAT has developed a methodology for in vivo monitoring of radioiodine in the thyroid of exposed individuals in case of emergency. Thyroid–neck phantoms of different sizes are required for calibrating the detection systems in appropriate counting geometries for the measurement of exposed population. A Low-Energy Germanium (LEGe) detector and a Fastscan Counter were calibrated using a set of thyroid phantoms fabricated by CIEMAT. Each neck phantom consists of a Lucite cylinder with a vial source of 131I. Counting efficiencies depending on age and thyroid sizes were obtained to be used to determine the activity of 131I in internally contaminated people. DL of 131I varies with the age, being in the range of 5–8 Bq for the LEGe detector and 26–42 Bq for the Fastscan. Detection of intakes resulting in Committed Effective doses far below 1 mSv are guaranteed for thyroid monitoring in a few days after the accidental exposure assuming a scenario of acute inhalation or ingestion of 131I by members of the public. INTRODUCTION In case of a nuclear accident large amounts of radioiodine may be released to the environment with the subsequent risk of contamination of the population. The thyroid gland is the target organ where de iodine is retained during few weeks after the intake took place. In vivo measurements of 131I in thyroid by gamma spectrometry are recommended to quickly identify the most contaminated people in an emergency scenario. The determination of the retained activity in the thyroid and the result internal dose estimate, help to decide about taking appropriate counter measures to avoid or minimize undesirable health effects due to the ionizing radiations. Germanium or NaI(Tl) detectors are commonly used for in vivo monitoring of exposed individuals at risk of incorporation of gamma emitters into the body. Radioactive sources of known activity in anthropomorphic phantoms simulating neck and contaminated thyroid gland of the individuals are required for calibration purposes. Lawrence Livermore National Laboratory (LLNL, USA) in collaboration with the European Radiation Dosimetry Group (EURADOS) organized in 2016 an international intercomparison on measurement and dose estimates of radioiodine deposited in the thyroid, using several (separate) sources of 131I and 125I in vials which were introduced in a ANSI neck phantom(1). In vivo counting facilities have developed calibration and measurement procedures for monitoring workers but a gap was identified after Fukushima NPP accident regarding available calibration protocols for children(2). The use of different phantoms simulating neck and thyroid of members of different groups of age are crucial for a proper calibration and accurate determination of the 131I activity in thyroid, in order to estimate reliable internal doses. The main goal of this work is to describe a methodology developed at CIEMAT Whole Body Counter (WBC) for the calibration and in vivo monitoring of 131I in the thyroid of contaminated adults and children. Thyroid phantoms of different sizes simulating children and adults were fabricated by CIEMAT following ICRP 89 recommendations(3). MATERIALS AND METHODS Detection systems CIEMAT Whole Body Counting facility counts with a Low-Energy Germanium (LEGe) detector system and a Fastscan (NaI(Tl)) Counter for in-vivo measurement of 131I in thyroid. The active area of each LEGe detector is 3800 mm2, with a diameter of 70 mm and a thickness of 25 mm, with a Carbon Epoxy window, 0.5 mm thick(4). The LEGe detectors are placed inside a shielded room of 13 cm steel walls lined with Pb, Cd and Cu with independent ventilation to reduce environmental background. LEGe detectors present an excellent resolution and good efficiency at low and moderate energies (10–1000 keV). One of the four LEGe is used for thyroid monitoring at a distance of 15 cm from the neck and for a counting time of 20 min (Figure 1). Figure 1. View largeDownload slide Thyroid monitoring using a LEGe detector inside a shielded room at CIEMAT WBC. Figure 1. View largeDownload slide Thyroid monitoring using a LEGe detector inside a shielded room at CIEMAT WBC. The Fastscan Counter was manufactured by Canberra Industries. It includes two large sodium iodine detectors (NaI(Tl)) of 7.6 cm × 12.7 cm × 40.6 cm along the vertical axis(5). The Fastscan whole body counter is designed to quickly and accurately monitor people for internal contamination of gamma-emitting radionuclides with energies between 100 keV and 2 MeV (Figure 2). Figure 2. View largeDownload slide Fastscan counter. Figure 2. View largeDownload slide Fastscan counter. Both systems are operating using Genie2000 Gamma Spectrometry software(6) which provides a complete set of operating procedures to perform calibration functions, to analyze subjects and for quality assurance operations. Design of the thyroid–neck phantom set A ‘family’ of neck–thyroid calibration phantoms for children (Figure 3) was fabricated at CIEMAT (Spain). Each phantom consists of a Lucite cylinder with a lateral cavity where the thyroid gland simulator is introduced. Each cylinder size was designed according to the age of the individual following ICRP 89 recommendations(3). The contaminated thyroid gland is simulated using a cylindrical vial filled with a homogeneously distributed liquid solution of 131I. The selected volumes of the different thyroid glands are 1.8, 3.4, 7.7, 12 ml, which correspond to 1, 5, 10, 15-year-old children, respectively. Adult neck–thyroid phantom was designed according to ANSI 13.44(7) standard with a thyroid gland volume of 20 ml simulating reference male and 17 ml for reference female. Figure 3. View largeDownload slide CIEMAT neck–thyroid phantom set. Figure 3. View largeDownload slide CIEMAT neck–thyroid phantom set. The neck perimeters of the different phantoms were calculated based on anatomical measurements to different ages of children. The neck thickness of the phantoms was calculated from measurements of CT studies (Table 1). Table 1. Neck phantom sizes for different ages. Age (y) Perimeter (cm) Height (cm) 1 22 ± 2 7,1 ± 0,6 5 26 ± 3 8,2 ± 0,9 10 30 ± 4 10 ± 1 15 34 ± 5 11 ± 2 Age (y) Perimeter (cm) Height (cm) 1 22 ± 2 7,1 ± 0,6 5 26 ± 3 8,2 ± 0,9 10 30 ± 4 10 ± 1 15 34 ± 5 11 ± 2 Table 1. Neck phantom sizes for different ages. Age (y) Perimeter (cm) Height (cm) 1 22 ± 2 7,1 ± 0,6 5 26 ± 3 8,2 ± 0,9 10 30 ± 4 10 ± 1 15 34 ± 5 11 ± 2 Age (y) Perimeter (cm) Height (cm) 1 22 ± 2 7,1 ± 0,6 5 26 ± 3 8,2 ± 0,9 10 30 ± 4 10 ± 1 15 34 ± 5 11 ± 2 RESULTS AND DISCUSSION Efficiency calibration for different counting geometries of in vivo measurement of 131I in the thyroid (children and adults) were performed at the WBC of CIEMAT using Fastscan Counter and LEGe detector system. Fastscan Counter is used for a rapid measurement of thyroid activity in exposed individuals in case of radiological or nuclear emergency due to its excellent efficiency at medium and high energies. LEGe detectors are more suitable in case of complex cases of internal contamination due to their high resolution especially in a range of 10–1000 keV. Calibration sources In both detection systems (LEGe and Fastscan), efficiency calibration curves (counts/gamma) versus energy (keV) were obtained using 131I as calibration source for 1, 5, 10 and 15-year-old children and for the reference female. A mock-iodine of 133Ba and 137Cs was formerly used for the reference male calibration. All sources were manufactured and certificated by Laboratory of Ionizing Radiation Metrology (LMRI-CIEMAT) (Table 2). Table 2. Activities of the calibration sources. Date of certificate Age (y) A (kBq) ΔA (kBq), k = 2 10/07/2015 1 29,46 0,59 10/07/2015 5 29,79 0,6 10/07/2015 10 59,5 1,2 10/07/2015 15 49,9 1,0 31/10/2014 Woman 40.6 1,2 (2.8%) 10/07/2015 Man 18,81 0,38 Date of certificate Age (y) A (kBq) ΔA (kBq), k = 2 10/07/2015 1 29,46 0,59 10/07/2015 5 29,79 0,6 10/07/2015 10 59,5 1,2 10/07/2015 15 49,9 1,0 31/10/2014 Woman 40.6 1,2 (2.8%) 10/07/2015 Man 18,81 0,38 Table 2. Activities of the calibration sources. Date of certificate Age (y) A (kBq) ΔA (kBq), k = 2 10/07/2015 1 29,46 0,59 10/07/2015 5 29,79 0,6 10/07/2015 10 59,5 1,2 10/07/2015 15 49,9 1,0 31/10/2014 Woman 40.6 1,2 (2.8%) 10/07/2015 Man 18,81 0,38 Date of certificate Age (y) A (kBq) ΔA (kBq), k = 2 10/07/2015 1 29,46 0,59 10/07/2015 5 29,79 0,6 10/07/2015 10 59,5 1,2 10/07/2015 15 49,9 1,0 31/10/2014 Woman 40.6 1,2 (2.8%) 10/07/2015 Man 18,81 0,38 Calibration of LEGe detector for measurement of 131I in thyroid of adults and children An individual detector (Det 1) of the LEGe detection system placed inside the shielded room and positioned at a detector-thyroid distance of 15 cm was calibrated by both thyroid–neck phantom and radioactive sources simulating contaminated thyroid gland for each children and adults geometry performed(8). Figure 4 shows the counting efficiency (cps/γ) versus energy (keV) curves for the different counting geometries implemented. Figure 4. View largeDownload slide Counting geometry for thyroid calibration and counting efficiency versus energy for CIEMAT LEGe detector. Figure 4. View largeDownload slide Counting geometry for thyroid calibration and counting efficiency versus energy for CIEMAT LEGe detector. The efficiency value corresponding to the main emission of 131I (364 keV) is utilized in order to calculate activity in a possible intake. Table 3 shows the efficiency values for different sizes of thyroid glands. Table 3. Efficiency in LEGe detector for 364 keV. V (ml) Eff (cps/γ) 364 keV Δeff (cps/γ) 1,80 0,002375 5,14E-05 3,4 0,002411 4,88E-05 7,7 0,002310 4,62E-05 12 0,001981 6,70E-05 17 0,001970 9,93E-05 20 0,002801 9,93E-05 V (ml) Eff (cps/γ) 364 keV Δeff (cps/γ) 1,80 0,002375 5,14E-05 3,4 0,002411 4,88E-05 7,7 0,002310 4,62E-05 12 0,001981 6,70E-05 17 0,001970 9,93E-05 20 0,002801 9,93E-05 Table 3. Efficiency in LEGe detector for 364 keV. V (ml) Eff (cps/γ) 364 keV Δeff (cps/γ) 1,80 0,002375 5,14E-05 3,4 0,002411 4,88E-05 7,7 0,002310 4,62E-05 12 0,001981 6,70E-05 17 0,001970 9,93E-05 20 0,002801 9,93E-05 V (ml) Eff (cps/γ) 364 keV Δeff (cps/γ) 1,80 0,002375 5,14E-05 3,4 0,002411 4,88E-05 7,7 0,002310 4,62E-05 12 0,001981 6,70E-05 17 0,001970 9,93E-05 20 0,002801 9,93E-05 Calibrations of Fastscan Counter for the in vivo measurement of 131I in thyroid (adults and children) The calibration of Fastscan was carried out for standing up counting geometry(9). The neck–detector distance is 12 cm. The height to the thyroid depends on the age of individuals (Table 4) according to WHO and ANSI 13.30. Table 4. Source volume (ml) and ground-thyroid distance of the thyroid, CIEMAT Fastscan calibration. V (ml) Age (y) h (cm) 1,8 1 61,5 3,4 5 92,0 7,7 10 117,0 12 15 girl 138,5 12 15 boy 143,5 17 Woman 139,0 20 Man 156,5 V (ml) Age (y) h (cm) 1,8 1 61,5 3,4 5 92,0 7,7 10 117,0 12 15 girl 138,5 12 15 boy 143,5 17 Woman 139,0 20 Man 156,5 Table 4. Source volume (ml) and ground-thyroid distance of the thyroid, CIEMAT Fastscan calibration. V (ml) Age (y) h (cm) 1,8 1 61,5 3,4 5 92,0 7,7 10 117,0 12 15 girl 138,5 12 15 boy 143,5 17 Woman 139,0 20 Man 156,5 V (ml) Age (y) h (cm) 1,8 1 61,5 3,4 5 92,0 7,7 10 117,0 12 15 girl 138,5 12 15 boy 143,5 17 Woman 139,0 20 Man 156,5 Upper detector was calibrated for children aged 1 and 5 years, and upper detector for the rest of the set phantoms (Figure 5). Figure 5. View largeDownload slide Counting geometry for thyroid calibration and counting efficiency versus energy for CIEMAT Fastscan Counter. Figure 5. View largeDownload slide Counting geometry for thyroid calibration and counting efficiency versus energy for CIEMAT Fastscan Counter. The maximum of efficiency curves corresponds to the energy around 400 keV, close to the main emission of 131I (364 keV), which is noted in Table 5. Table 5. Efficiency in Fastscan superior detector in 364 keV. V (ml) Eff (cps/γ) 364 keV Δeff (cps/γ) 1,8 0,022834 8,81E-04 3,4 0,036963 1,41E-03 7,7 0,035254 1,48E-03 12 0,032312 1,19E-03 12 0,034102 2,10E-03 17 0,028840 1,69E-03 20 0,028798 1,69E-03 V (ml) Eff (cps/γ) 364 keV Δeff (cps/γ) 1,8 0,022834 8,81E-04 3,4 0,036963 1,41E-03 7,7 0,035254 1,48E-03 12 0,032312 1,19E-03 12 0,034102 2,10E-03 17 0,028840 1,69E-03 20 0,028798 1,69E-03 Table 5. Efficiency in Fastscan superior detector in 364 keV. V (ml) Eff (cps/γ) 364 keV Δeff (cps/γ) 1,8 0,022834 8,81E-04 3,4 0,036963 1,41E-03 7,7 0,035254 1,48E-03 12 0,032312 1,19E-03 12 0,034102 2,10E-03 17 0,028840 1,69E-03 20 0,028798 1,69E-03 V (ml) Eff (cps/γ) 364 keV Δeff (cps/γ) 1,8 0,022834 8,81E-04 3,4 0,036963 1,41E-03 7,7 0,035254 1,48E-03 12 0,032312 1,19E-03 12 0,034102 2,10E-03 17 0,028840 1,69E-03 20 0,028798 1,69E-03 Validation of the 131I monitoring calibration for adults and children The validation of the thyroid calibration was carried out using the same thyroid phantom set and vials but with different radionuclides. Liquid sources of 133Ba (90%) and 137Cs (10%) were used for the simulation of 131I emissions. Table 6 summarizes the activities and Type A uncertainties (Δ) of the different mocks used. Each vial was introduced in the corresponding neck phantom, placed at the same conditions of the calibration geometry. Five measurements were performed for each phantom representing 1, 5, 10 and 15-year-old children, reference male and female adults. Table 6. Activities of the mock sources with 133Ba and 137Cs. V (ml) 133Ba A (Bq) 133Ba ΔA (Bq) 137Cs A (Bq) 137Cs ΔA (Bq) 1,83 9458,8 14,8 942,11 2,89 3,43 9454,3 14,8 941,67 2,89 7,63 9493,6 14,9 945,58 2,90 12,03 9531,3 14,9 949,33 2,91 17,03 9488,7 14,9 945,09 2,90 V (ml) 133Ba A (Bq) 133Ba ΔA (Bq) 137Cs A (Bq) 137Cs ΔA (Bq) 1,83 9458,8 14,8 942,11 2,89 3,43 9454,3 14,8 941,67 2,89 7,63 9493,6 14,9 945,58 2,90 12,03 9531,3 14,9 949,33 2,91 17,03 9488,7 14,9 945,09 2,90 Table 6. Activities of the mock sources with 133Ba and 137Cs. V (ml) 133Ba A (Bq) 133Ba ΔA (Bq) 137Cs A (Bq) 137Cs ΔA (Bq) 1,83 9458,8 14,8 942,11 2,89 3,43 9454,3 14,8 941,67 2,89 7,63 9493,6 14,9 945,58 2,90 12,03 9531,3 14,9 949,33 2,91 17,03 9488,7 14,9 945,09 2,90 V (ml) 133Ba A (Bq) 133Ba ΔA (Bq) 137Cs A (Bq) 137Cs ΔA (Bq) 1,83 9458,8 14,8 942,11 2,89 3,43 9454,3 14,8 941,67 2,89 7,63 9493,6 14,9 945,58 2,90 12,03 9531,3 14,9 949,33 2,91 17,03 9488,7 14,9 945,09 2,90 A proficiency test was carried out in order to evaluate ‘Relative Bias’ and ‘Repeatability’ parameters according to ISO/IEC 28 218 Standard(10). Results for both detection systems (LEGe and Fastscan) were in compliance with acceptance criteria of ISO 28 218 parameters, relative bias (Br) is between [−0.25, 0.5] and repeatability (SBr) is <0.4. Sensitivity of the detection systems for thyroid monitoring. Detection limit According to ISO/IEC 28 218(10) the value of the detection limit (DL) indicates the ability of the in vivo laboratory to detect a radionuclide incorporated by an individual and deposited in total body or in organs. The DL is mainly dependent on the person (tissue thickness attenuation), the measurement geometry, the efficiency and counting time. DL can be calculated from the measurement of a blank person or a blank phantom (Figure 6) as follows: LD=2k1−α(1t·ε)2(p2mn0+(p2m)2n0)+k21−α(1t·ε)1−k21−α(u(ε)(ε))2 where n0 = # counts in the Surface B1 and B2; p = # channels of the neck; m = # channels in the Surface B1 and B2; ε = efficiency; u(ε) = efficiency uncertainty; and k1−α = 1.645. Figure 6. View largeDownload slide Detection limit (DL). Figure 6. View largeDownload slide Detection limit (DL). In both (LEGe and Fastscan) detection systems DL was calculated by each counting geometry using neck phantom and blank thyroid gland in routine measurement conditions (Tables 7 and 8). Table 7. Detection limits of 131I in thyroid for different configurations of LEGe detector. DL Detector 1 LEGe, t = 1200 s, d = 15 cm Age (y) 1 5 10 15 Woman Man DL (Bq) 6,1 4,6 5,3 6,2 7,9 6,4 DL Detector 1 LEGe, t = 1200 s, d = 15 cm Age (y) 1 5 10 15 Woman Man DL (Bq) 6,1 4,6 5,3 6,2 7,9 6,4 Table 7. Detection limits of 131I in thyroid for different configurations of LEGe detector. DL Detector 1 LEGe, t = 1200 s, d = 15 cm Age (y) 1 5 10 15 Woman Man DL (Bq) 6,1 4,6 5,3 6,2 7,9 6,4 DL Detector 1 LEGe, t = 1200 s, d = 15 cm Age (y) 1 5 10 15 Woman Man DL (Bq) 6,1 4,6 5,3 6,2 7,9 6,4 Table 8. Detection limits of 131I in thyroid for different configurations of Fastscan Counter. DL Fastscan, t = 300 s, d = 12 cm Age (y) 1 5 10 15 girla 15 boya Woman Man DL (Bq) 41,9 26,1 25,6 27,8 36,2 31,7 33,8 DL Fastscan, t = 300 s, d = 12 cm Age (y) 1 5 10 15 girla 15 boya Woman Man DL (Bq) 41,9 26,1 25,6 27,8 36,2 31,7 33,8 aThey are the same phantom and their heights of measurement in the Fastscan are different, which are referenced in Table 4. Table 8. Detection limits of 131I in thyroid for different configurations of Fastscan Counter. DL Fastscan, t = 300 s, d = 12 cm Age (y) 1 5 10 15 girla 15 boya Woman Man DL (Bq) 41,9 26,1 25,6 27,8 36,2 31,7 33,8 DL Fastscan, t = 300 s, d = 12 cm Age (y) 1 5 10 15 girla 15 boya Woman Man DL (Bq) 41,9 26,1 25,6 27,8 36,2 31,7 33,8 aThey are the same phantom and their heights of measurement in the Fastscan are different, which are referenced in Table 4. Estimation of committed doses for the exposed population in emergency scenarios Committed effective dose for children (E(70)) and adults (E(50)) have been estimated taking into account the values of DL (Bq) for 131I that were obtained for both detection systems (LEGe and Fastscan) for the different counting geometries implemented. The scenarios of internal exposure considered are acute inhalation of 131I type F and acute ingestion. Measurements are supposed to be performed three days after intake. Activity detected is assumed to be the same as the DL (Bq) for 131I and the committed effective dose was estimated. The results confirm that three days after the intake, the in vivo measurement of 131I in thyroid for the exposed population applying the methodology developed by CIEMAT WBC allows estimating doses about tens of microSievert for a short counting time of 300 s. CONCLUSIONS CIEMAT Whole Body Counting Laboratory has developed a calibration methodology for the in vivo measurement of 131I in the thyroid of exposed population (adults and children). A Fastscan Counter and a LEGe detector inside a shielded room are used for this purpose. A set of neck phantoms for thyroid calibration were manufactured at CIEMAT using Lucite with density and attenuation similar to soft tissue, on the basis of ICRP 89 and ANSI 13.44 recommendations for 1, 5, 10 and 15 years old children and adult male and female. Iodine-131 was used as calibration source. Calibration efficiency values depend mainly on the source volume, neck phantom–detector distance, relative detector-source position and attenuation due to neck thickness. Counting efficiency using Fastscan (5 min as counting time) is greater than the one for LEGe detector (20 min) for the same configuration. LEGe detector is suitable in case of complex internal contamination due to the excellent resolution of this equipment allowing the correct identification and quantification of different isotopes emitting similar gamma emissions. CIEMAT WBC has validated this in vivo method for thyroid monitoring which can be applied in case of radiological or nuclear emergency involving accidental intake of 131I through inhalation or ingestion by workers and members of the public of different ages. DL varies with the age of individuals, being in the range of 5–8 Bq of 131I for the LEGe detector and 26–42 Bq for the Fastscan Counter. Detection of intakes resulting in committed effective doses far below 1 mSv are guaranteed for thyroid monitoring in a few days after the accidental exposure assuming an scenario of acute inhalation or ingestion of 131I by members of the public. CIEMAT WBC has participated in the 2016 EURADOS/LLNL intercomparison of thyroid monitoring and dose evaluation to validate new ANSI thyroid phantom(11) and is currently involved in the Cathymara project ‘Child and Adult Thyroid Monitoring After Reactor Accident’ (OPERRA, 7FP EURATOM, 2016–17). ACKNOWLEDGEMENT Eduardo Garcia Toraño and Virginia Peyres from Metrology Laboratory, Inmaculada Sierra and Carolina Hernandez from In vitro Bioassay Laboratory and Infrastructure Division of CIEMAT for their contribution in the fabrication of the thyroid–neck phantom set and the preparation of radioactive sources. REFERENCES 1 Hickman , D. P. et al. . Thyroid phantom measurements in Joint EURADOS-LLNL intercomparison exercise . Radiat. Prot. Dosim. 178 ( 2 ), 152 – 159 ( 2018 ). Google Scholar CrossRef Search ADS 2 Lopez , M. A. et al. . Lessons learned from the EURADOS survey on individual monitoring data and internal dose assessments of foreigners exposed in Japan following the Fukushima Daiichi NPP accident . Radiat. Prot. Dosim. 170 ( 1–4 ), 402 – 406 ( 2016 ). Google Scholar CrossRef Search ADS 3 ICRP . Basic anatomical and physiological data for use in radiological protection reference values. ICRP Publication 89 . Ann. ICRP 32 ( 3–4 ), 225 – 227 ( 2002 ). 4 López Ponte , M. A. and Bravo , T. N. A Low Energy Germanium Detector System for lung counting at the WBC facility of CIEMAT . Radiat. Prot. Dosim. 89 ( 3–4 ), 221 – 227 ( 2000 ). Google Scholar CrossRef Search ADS 5 Canberra . Manual Fastscan Counter ( 2004 ). 6 Canberra . Manual Genie/Abacos 2000 ( 1999 ). 7 American National Standards Institute . I., ANSI/HPS N13.44–2014. Thyroid Phantom Used in Occupational Monitoring ( 2014 ). 8 Pérez López , B. and Navarro Amaro , J. F. Determinación in-vivo de I-131 en tiroides mediante el sistema LEGe Detector 1., CIEMAT/DR/DPI/08/13, Editor. 2013 , CIEMAT. 9 Pérez López , B. and Navarro Amaro , J. F. Determinación in-vivo de I-131 en tiroides mediante los sistemas NaI(Tl) y Fastscan, CIEMAT/DR/DPI/07/13, Editor. 2013 , CIEMAT. 10 ISO . ISO 28218: Radiation protection—performance criteria for radiobioassay, ISO, Editor. 2010 . p. 45. 11 Etherington , G. et al. . CAThyMARA report: technical guidelines for radioiodine in thyroid monitoring. OPERRA Deliverable D5.31 ( 2017 ). © The Author(s) 2018. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)

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Radiation Protection DosimetryOxford University Press

Published: Mar 23, 2018

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