In the case of a nuclear accident with a large release of the radionuclides into the environment, the main concern is exposure to the residents living in the vicinity of the accident site. This paper presents the development of a new thyroid monitor for such measurements and the results from phantom-based experiments.
Radiation Measurements 150 (2022) 106683 Contents lists available at ScienceDirect Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas Development of a new hand-held type thyroid monitor using multiple GAGG detectors for young children following a nuclear accident Kazuaki Yajima a, Eunjoo Kim a, *, Kotaro Tani a, Masumi Ogawa a, b, Yu Igarashi a, Munehiko Kowatari a, Osamu Kurihara a a National Institutes of Quantum and Radiological Science and Technology, National Institute of Radiological Sciences (QST− NIRS), 4-9-1 Anagawa, Inage-ku, Chiba, 263-8555, Japan Self-Defense Forces, Central Hospital, 1-2-24 Ikejiri, Setagaya-ku, Tokyo, 154-0001, Japan b A R T I C L E I N F O A B S T R A C T Keywords: Thyroid exposure Radioiodine Thyroid monitor GAGG detector Nuclear accident One of the most important lessons learned from the Fukushima Daiichi Nuclear Power Plant accident is that direct (in vivo) measurements of thyroid exposure to radioiodine (mainly, 131I) in the affected populations should be initiated in a timely manner Furthermore, the existing commercial detectors are not necessarily suitable for the measurement of young children, who are especially vulnerable to radiation exposure and therefore important to screen This paper presents the development of a new thyroid monitor for such measurements and the results from phantom-based experiments The monitor has two unique probes having multiple high-energy-resolution type Gd3(Al,Ga)5O12(Ce) (GAGG) detectors that can be placed directly on the young subject’s anterior neck The crystal size of the GAGG detector is cm3, and a probe consisting of a × or × detector array can be selected depending on the subject’s body size The thickness of the × array probe is 24 mm, which is less than that for a conventional NaI(Tl) survey meter having a crystal inch in diameter and inch long (38 mm) Experimental and computational calibrations of the new monitor using existing and virtual phantoms allowed us to determine the full energy peak efficiency for the 131I thyroid contents of different age groups from 3-mo-old to 10-yr-old and minimum detectable activity (MDA) values under various conditions As a result, the attainable MDA for subjects age ≤5 years under a normal background level (~0.05 μSv h− 1) was found to be ~30 Bq, which was low enough to identify children with thyroid-equivalent doses over 10 mSv up to about 25 days after the 131I intake Our new monitor would be useful in direct thyroid measurements for vulnerable young children following a large nuclear accident Introduction In the case of a nuclear accident with a large release of the radio nuclides into the environment, the main concern is exposure to the residents living in the vicinity of the accident site In particular, atten tion should be paid to the internal thyroid exposure to children due to intake of radioiodine, as demonstrated in the Chernobyl nuclear acci dent in 1986 (Cardis et al., 2011) The largest contributor to the internal thyroid dose is 131I, with a physical half-life of about days The dose delivered following intake of radioiodine is localized in the thyroid, a relatively small organ in the human body The thyroid dose per unit of 131 I intake (Sv Bq− 1) is much higher in young children than in adults, in accord with the thyroid mass defined in each age group’s anatomical model (e.g., 1.78 g for 1-yr-olds, 20.0 g for adults) (ICRP 1995, International Commission on Radiological Protection, 1998) The actual thyroid doses would be less age-dependent in the same exposure con dition because inhalation or ingestion intake amounts are smaller for younger people; however, it should be noted that the radiosensitivity of the thyroid per unit dose (e.g., the excess relative risk: ERR) was shown to be high in young children by epidemiological studies related to the Chernobyl accident (Brenner at al., 2011) In the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident that occurred in March 2011, the number of direct thyroid measurements to determine individuals’ 131I thyroid contents was very limited in contrast to that in the Chernobyl accident (Kim and Kurihara 2020) Therefore, the assessment of thyroid doses to most of Fukushima prefecture’s res idents had to be performed using other data, such as whole-body counter measurements targeting 134Cs and 137Cs, radiation monitoring results of * Corresponding author E-mail address: kim.eunjoo@qst.go.jp (E Kim) https://doi.org/10.1016/j.radmeas.2021.106683 Received 12 July 2021; Received in revised form November 2021; Accepted 17 November 2021 Available online 19 November 2021 1350-4487/© 2021 The Authors Published by Elsevier Ltd This is an open (http://creativecommons.org/licenses/by-nc-nd/4.0/) access article under the CC BY-NC-ND license K Yajima et al Radiation Measurements 150 (2022) 106683 food and drink items, atmospheric transport and dispersion model simulations for the released radionuclides, and so on (Hosoda et al., 2013; Kim et al., 2016; Ohba et al., 2020) Great effort has been expended on these dose assessments, which found that residents’ thy roid doses were very unlikely to exceed a thyroid-equivalent dose (TED) of 100 mSv and were mostly less than 20–30 mSv, even for children in the relatively high-dose regions (Kim and Kurihara 2020) However, the actual thyroid doses to individuals can be confirmed only from direct (i e., in vivo) measurements, despite the existence of uncertainties about the nature of radiation measurements, the intake scenario, and so on Ecological-model approaches using environmental data (e.g., air con centration, ground deposition density) involve still larger uncertainties and need to be verified by results of direct measurements This is one of the critical lessons learned from the FDNPP accident: namely, individual photon detection to assess thyroid exposure to the possibly affected populations must be performed in a timely manner so as not to miss the window for evidence of 131I intake in the case of a major nuclear acci dent event One technical problem in direct thyroid measurements is that existing photon detectors are not necessarily appropriate for measure ments of young children or newborns (Broggio et al., 2019) We found that a NaI(Tl) survey meter with a probe, in which a crystal of inch diameter and inch length is installed, was too bulky to be placed in close proximity to the anterior neck of preschool children (age 5 years old Development of the new thyroid monitor The system for the new thyroid monitor has been described in our previous paper (Yajima et al., 2020) It uses commercially available GAGG detectors (Model: HR-GAGGG1C1C1C-type, Clear-Pulse Co., Tokyo Japan) enclosed in originally designed and manufactured Fig Scenes of mock-up experiments performed to identify the optimal detector arrangements for the new thyroid monitor K Yajima et al Radiation Measurements 150 (2022) 106683 Fig Exterior views of the new thyroid monitor (Panel A: the probe for × detector array, Panel B: the probe for × detector array) The dimensions are the same in the two pictures radioactivity We also performed a computational calibration using age-specific mathematical phantoms (3-mo-old, 1-yr-old, 5-yr-old, and 10-yr-old) to cover broader age groups The mathematical phantoms have been described elsewhere (Ulanovsky and Eckerman, 1998) and were kindly supplied by Dr A.V Ulanovsky at our request It is noted that the thyroid-shaped containers in the IRSN phantoms were designed with reference to the configurations of these mathematical phantoms The computational calibration was performed only for the detector arrangement of the × array through a series of simulations using the Monte Carlo N-Particle® code ver (MCNP6) (Werner, 2017) In the simulations, the internal structure of the GAGG detectors was modeled for the thyroid monitor, and the number of photons emitted was set to be large enough to reduce the relative standard deviation to 10%, photon energy >100 keV) to the primary peak line of 131I (365 keV, 81.7%) were from 132Te (228 keV, 88.0%) and 132I (523 keV, 16.0%) Our new thyroid monitor thus has sufficient energy resolution to observe each of these three peak lines on a pulse height spectrum without interference from the other two peak lines The advantages of the GAGG detectors are described above in Section In particular, the significant gain-shift due to the variation of temperature at a measurement place can be a common problem in scintillation detectors The GAGG detectors used in the new monitor solve this problem by fine gain adjustments based on characteristic tests, and the detectors are also reliable for the use of new thyroid monitor Our new monitor is intended to be used with a contact geometry against the neck; however, it is important to examine the measurement uncertainty due to the probe’s likely displacement, especially as the target subjects are young children This study examined one of the pri mary uncertainty factors, the variation of the FEP efficiency due to the probe’s displacement As demonstrated in Fig 6− 8, this variation was found to be relatively small for the vertical/lateral displacements, but was expected to be rather significant if there is a continuous gap between the probe and the neck during measurements of subjects We estimated that the uncertainty due to the probe’s displacement is within ~20% in practical use (i.e., assuming a gap of a few millimeters between the probe and the subject’s neck and some other minor displacements) Larger displacements of the probe would appear to be abnormal by eye and were not assumed here However, actual measurements will also be accompanied with the counting statistics, the measurement uncertainty due to the inter-individual differences in the thyroid volume and thyroid-overlying tissue thickness (Likhtarev et al., 1995; Ulanovsky et al., 1997), and so on To reduce the measurement uncertainty, the counting distance needs to be maximized, as suggested by the previous studies (Kramer and Crowley, 2000; Beaumont et al., 2018); however, there is a trade-off relationship with the sensitivity A long counting distance is beneficial if the subject’s body has been heavily exposed to radionuclides (IAEA, 1988), in particular in the case of direct mea surements at the thyroid, in which the exact location of this small organ is not visible from outside the body The experiences gained from the FDNPP accident suggest that situations in which members of the public are overexposed in a nuclear accident are unlikely to happen, as long as appropriate radiation protection measures are taken in a timely manner; however, all conceivable situations should be considered for the response to a future nuclear disaster The evaluated MDA values (Figs and 10) are useful to estimate the period of time during which direct thyroid measurements targeting 131I are feasible, given its relatively short physical half-life and biological half-life in particular for young children (ICRP 1989) Our new thyroid monitor achieved an MDA value of ~30 Bq for a counting time of 180 s under normal background conditions, which was comparable to that by K Yajima et al Radiation Measurements 150 (2022) 106683 Fig 10 MDA for the 131I thyroid contents as a function of the ambient dose rate in the case of a measurement time of 180 s (Panel A for × detector array, Panel B for × detector array) a NaI(Tl) spectrometer with a 1-inch-dia., 1-inch thick crystal in similar experiments (Yajima et al., 2020) It is notable that the total volume that is sensitive to radiation is much smaller in the new thyroid monitor (4 or cm3) compared to this NaI(Tl) spectrometer (12.9 cm3) On the other hand, the MDA was ~40 Bq for a stationary-type thyroid monitor equipped with a high-purity germanium (HPGe) semiconductor detector mounted in a 50-mm-thick annular-shaped lead shield at our institute (Kunishima et al., 2019; NIRS, 2016), although this monitor was difficult to be applied to children Fig 12 illustrates the TEDs corresponding to the MDA value for different age groups as a function of the time after intake: Panel A for the normal background and Panel B for the elevated background The MDA values are described in Section 4.3 Here we assumed that the physi ochemical form was elemental iodine and used the datasets of the agespecific thyroid 131I retention rates (Bq per Bq Intake) taken from the MONDAL code (Ishigure et al., 2004) to prepare the figure The MON DAL code has the database of retention/excretion rates for 42 radionu clides included in ICRP Publication 54 (International Commission on Radiological Protection, 1989) and 78 (International Commission on Radiological Protection, 1997) and was validated by comparisons with the data on these references Based on this result, it is expected that thyroid exposure corresponding to 10 mSv in TED for the 1-yr-old age group can be detected until about 25 days post intake under a normal background level of 0.05 μSv h− (or until 10 days post intake under an elevated background condition at 2.5 μSv h− 1) The same estimation can be applied to the other age groups using the figure, with the result that the older an age group is, the longer the period is These periods could be regarded as an index for the time limitation of direct thyroid measure ments with the new thyroid monitor for each age group, although the Fig 11 Scenes of mockup measurements with the new thyroid monitor periods vary with the dose level of concern The direct thyroid mea surements should be initiated in a timely manner as noted in the Introduction; however, some delay would be unavoidable in scenarios in which a significant release of radionuclides lasts >1 week and residents living in the affected areas are then ordered to shelter indoors by au thorities during the release The period available for the measurements would thus be expected to be shortened (especially for young children), and the prioritization of subjects should be considered using the above estimations It is desirable that direct thyroid measurements are performed at places with as low as possible ambient dose rates The 2013 IAEA guideline recommends that the ambient dose rate at the measurement location be less than 0.2 μSv h− However, this was difficult to imple ment in the screening campaigns conducted to identify the levels of internal thyroid exposure to children at the end of March 2011, about two weeks after the accident (Kim et al., 2012) Considerable elevations of background radiation level can occur across vast territories after a large-scale nuclear accident; indeed, this is considered one of the major obstacles for the early initiation of direct thyroid measurements Finally, we would like to address the advantages of our new monitor over existing devices First, the unique probe shape allows stabilization against the curved surface of the neck during measurements of young children Second, the multiple detector system allows identification of irregular deposition of iodine in the thyroid (e.g., a difference between the left and right lobes) if necessary Third, the variation of the FEP K Yajima et al Radiation Measurements 150 (2022) 106683 future Summary We developed a new hand-held type thyroid monitor to measure radioiodine in the human thyroid in the case of a major nuclear accident The main target subjects of this monitor are young children including newborns Multiple small GAGG detectors with 1-cm cube-shaped crystals in each were arranged along the neck surface, and two detec tor arrangements (4 × and × detector arrays) were finally selected based on mock-up experiments The narrow thickness of the × de tector array probe (24 mm) allowed for contact placement on the anterior neck of the 1-yr-old mathematical phantom The full energy peak efficiency (FEP) of the monitor for 131I (at 365 keV) in the thyroid was obtained by experiments using IRSN phantoms and simulations using mathematical phantoms Based on the results, minimum detect able activity (MDA) was evaluated for various ages The MDA values for subjects aged ≤5-yr-old were estimated as ~30 Bq at a normal back ground level for a counting time of 180 s This value would be adequate to detect the 131I thyroid content in 1-yr-old children corresponding to a thyroid-equivalent dose of 10 mSv until about 25 days post intake The possible variation of the FEP values due to the displacement of the probe was estimated to be about 20% Our monitor would be useful for direct thyroid measurements of young children following a major nuclear accident Funding This work was financially supported by the Nuclear Regulation Au thority of Japan under the Radiation Safety Research Promotion Fund (JPJ007057) Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper Fig 12 Thyroid-equivalent doses (TEDs) corresponding to the MDA for different age groups as a function of the time after intake via inhalation of 131I in the form of elemental iodine (Panel A for the normal background: 0.05 μSv h− 1, Panel B for the elevated background: 2.5 μSv h− 1) The MDA values for each condition are described in Section 4.3 Acknowledgements We would like to express our gratitude to Dr Susumu Yokoya of Fukushima Medical University and Dr Nao Nishimura of National Center for Child Health and Development for their valuable comments on direct thyroid measurements of young children We also appreciate Drs Tiffany Beaumont and David Broggio of IRSN for their support regarding the development and delivery of the phantom sets and Dr Alexander Ulanovsky for providing MCNP’s input decks for his devel oped mathematical phantoms efficiency is expected to be small for children aged ≤5 yrs (Fig 5) The experimental FEP efficiency for the 5-yr-old IRSN phantom can be applied to the FEP efficiency for younger children; the calculated peak efficiencies for the 3-mo-old age group and the 1-yr-old age group were about 20% higher (Fig 5), resulting in reasonable overestimations of the 131I thyroid content We currently consider that the best use of our monitor is the addi tional or detailed measurements in combination with screening using NaI(Tl) survey meters (e.g., TCS-171/172) at the venue designated on the regional evacuation plan for each nuclear power plant site Potential subjects for the monitor are supposed to be persons (in particular, young children) whose internal thyroid doses are found to be higher than a certain dose level (e.g., 50 mSv in TED) Comparative measurements of the same subjects by the two methods would surely be useful to validate the results of the screening for dealing with large populations Nonspectrometric devices would offer accurate determinations of the 131I thyroid content based on appropriate calibration (Isaksson et al., 2019), although one should evaluate the interference of other radionuclides in measurements In this regard, a dose rate meter recently developed for thyroid monitoring is also of interest to improve the early response in a nuclear disaster (Meisenberg and Gerstmann, 2017) We will describe further considerations on the use of our new thyroid monitor in the References Beaumont, T., Ideias, P.C., Rimlinger, M., Broggio, D., Frank, D., 2017 Development and test of sets of 3D printed age-specific phantoms for 131I measurements Phys Med Biol 72, 4673–4693 https://doi.org/10.1088/1361-6560/aa6514, 2017 Beaumont, T., Rimliger, M., Broggio, D., Ideias, P.C., Frank, D., 2018 A systemic experimental study of parameters influencing 131-iodine in vivo spectrometric measurements using age-specific thyroid phantoms J Radiol Prot 38, 651–655 https://doi.org/10.1088/1361-6498/aab967 Brenner, A.V., Tronko, M.D., Hatch, M., Bogdanova, T.I., Oliynik, V.A., Lubin, J.K., Zablotska, L.B., Tereschenko, V.P., McConnell, R.J., Zamotaeva, G.A., O’Kane, P., Bouville, A.C., Chaykovskaya, L.V., Greenebaum, E., Paster, I.P., Shpak, V.M., Ron, E., 2011 I-131 dose response for incident thyroid cancers in Ukraine related to the Chernobyl accident Environ Health Perspect 119 (7), 933–939 https://doi org/10.1289/ehp.1002674 Broggio, D., Baud´e, D., Belchior, A., Berkovskyy, V., Bonchuck, Y., Dewogh elaăere, J., Etherington, G., Fojtớk, P., Franck, D., Gomez-Ros, J.M., Gregoratto, D., Helebrant, J., H´ eriard Dubreuil, G., Hůlka, J., Isaksson, M., Kocsonya, A., Lebacq, A.L., Likhtarev, I., Lombardo, P., Lopez, M.A., Mal´ atov´ a, I., Marsh, J.W., Mitu, I., Monteiro Gil, O., Moraleda, M., Navarro, J.F., O´sko, J., P´ antya, A., P´ azm´ andi, T., Perez, B., Pospisil, V., Ratia, G., Saizu, M.-A., Sz´ ant´ o, P., Teles, P., Tymi´ nska, K., K Yajima et al Radiation Measurements 150 (2022) 106683 Vanhavere, F., Vaz, P., Vrba, T., Vu, I., Youngman, M., Zagyvai, P., 2019 Child and adult thyroid monitoring after a reactor accident (CAThyMARA): technical recommendations and remaining gaps Radiat Meas 128, 106069 https://doi.org/ 10.1016/j.radmeas.2019.02.008 Cardis, E., Hatch, M., 2011 The Chernobyl accident − an epidemiological perspective Clin Oncol 23 (4), 251–260 https://doi.org/10.1016/j.clon.2011.01.510 Currie, L.A., 1968 Limits for qualitative detection and quantitative determination Application to radiochemistry Anal Chem 40 (3), 586–593 https://doi.org/ 10.1021/ac60259a007 Gilmore, G., 2008 Practical Gamma-Ray Spectrometry, second ed Wiley, New York, ISBN 9780470861967 Hosoda, M., Iwaoka, K., Tokonami, S., Tamakuma, Y., Shiroma, Y., Fukuhara, T., Mayo, Y., Taniguchi, J., Akata, N., Osanai, M., Tsujiguchi, T., Yamaguchi, M., Kashiwakura, I., 2019 Comparative study of performance using different gamma-ray spectrometer for thyroid monitoring under emergency situations Health Phys 116 (1), 81–87 https://doi.org/10.1097/hp.0000000000000954 Hosokawa, Y., Hosoda, M., Nakata, A., Kon, M., Urushizaka, M., Yoshida, M.A., 2013 Thyroid screening survey on children after the Fukushima Daiichi nuclear power plane accident Rad Emerg Med (1), 82–86 http://crss.hirosaki-u.ac jp/wp-content/files_mf/1465542161vol2_ rem_13_yoichirohosokawa.pdf International Atomic Energy Agency, 1988 The Radiological Accident in Goiˆ ania https ://www-pub.iaea.org/MTCD/Publications/PDF/Pub815_web.pdf International Atomic Energy Agency, 2013 Actions to Protect the Public in an Emergency Due to Severe Conditions at a Light Water Reactor EPR-NPP PUBLIC PROTECTIVE ACTIONS, 2013 https://www-pub.iaea org/MTCD/Publications/PDF/EPR-NPP_PPA_ web.pdf International Commission on Radiological Protection, 1989 Individual monitoring for intakes of radionuclides by workers ICRP Publication 54 Ann ICRP 19 (1− 3) International Commission on Radiological Protection, 1995 Age-dependent doses to the members of the public from intake of radionuclides: part inhalation dose coefficients ICRP Publication 71 Ann ICRP 25 (3− 4) International Commission on Radiological Protection, 1997 Individual monitoring for internal exposure of workers ICRP Publication 78 Ann ICRP 27 (3− 4) International Commission on Radiological Protection, 1998 ICRP Database of Dose Coefficients: Workers and Members of the Public version Isaksson, M., Broggio, D., Fojtík, P., Lebacq, A.L., Navarro Amaro, J.F., O´sko, J., P´erez L´ opez, B., Vu, I., Battisti, P., Bă orjesson, J., Carlsson, M., Castellani, C.M., Gồrdestig, M., Hill, P., Krajewska, G., Lỹnendonk, G., Meisenberg, O., Stenstră om, M., El Mantani Ordoulidis, S., 2019 Assessing 131I thyroid by non-spectrometric instruments ‒ A European intercomparison exercise Radiat Meas 128, 106115 https://doi.org/10.1016/j.radmeas.2019.04.018 Ishigure, N., Matsumoto, M., Nakano, T., Enomoto, H., 2004 Development of software for internal dose calculation from bioassay measurements Radiat Protect Dosim 109 (3), 235–242 https://doi.org/10.1093/rpd/nch048 Japan Atomic Energy Research Institute, 1993 Health Physics in JAERI JAERI-M-93172 https://jopss.jaea.go.jp/pdfdata/JAERI-M-93-172.pdf Khrutchinsky, A., Drozdovitch, V., Kutsen, S., Minenko, V., Khrouch, V., Luckyanov, N., Voillequ´ e, P., Bouville, A., 2012 Mathematical modeling of a survey-meter used to measure radioactivity in human thyroids: Monte Carlo caluclations of the device response and uncertainties Appl Radiat Isot 70, 743–751 https://doi.org/ 10.1016/j.apradiso.2011.12.032 Kim, E., Kurihara, O., 2020 Thyroid doses in children from radioiodine following the accident at the Fukushima Daiichi nuclear power plant J Radiat Prot Res 45 (1), 2–10 https://doi.org/10.14407/jrpr.2020.45.1.2 Kim, E., Kurihara, O., Suzuki, T., Matsumoto, M., Fukutsu, K., Yamada, Y., Sugiura, N., Akashi, M., 2012 Screening survey on thyroid exposure for children after the Fukushima Daiichi nuclear power station accident In: Proceedings of the First NIRS Symposium on the Reconstruction of Early Internal Dose in the TEPCO Fukushima Dai-Ichi Nuclear Power Station Accident National Institute of Radiological Sciences, Chiba, Japan, pp 59–66 NIRS-M-252 https://repo.qst.go.jp/?action=pages_vie w_main&active_action=repository_view_ main_item_detail&item_id=73765&ite m_no=1&page_id=13&block_id=21 Kim, E., Kurihara, O., Tani, K., Ohmachi, Y., Fukutsu, K., Sakai, K., Akashi, M., 2016 Intake ratio of 131I to 137Cs derived from thyroid and whole-body doses to Fukushima residents Radiat Protect Dosim 168 (3), 408–418 https://doi.org/10.1097/ hp.0000000000001345 Kim, E., Yajima, K., Hashimoto, S., Tani, K., Igarashi, Y., Iimoto, T., Ishigure, N., Tatsuzaki, H., Akashi, M., Kurihara, O., 2020 Reassessment of internal thyroid doses to 1,080 children examined in a screening survey after the 2011 Fukushima nuclear disaster Health Phys 118 (1), 36–52 https://doi.org/10.1097/ hp.0000000000001125 Kramer, G.H., Crowley, P., 2000 The assessment of the effect of thyroid size and shape on the activity estimate using Monte Carlo simulation Health Phys 78 (6), 727–738 https://doi.org/10.1097/00004032-200006000-00018 Kunishima, N., Tani, K., Kurihara, O., Kim, E., Nakano, T., Kishimoto, R., Tsuchiya, H., Omatsu, T., Tatsuzaki, H., Tominaga, T., Watanabe, S., Ishigure, N., Akashi, M., 2019 Numerical simulation based on individual voxel phantoms for a sophisticated evaluation of internal doses mainly from 131I in highly exposed workers involved in the TEPCO Fukushima Daiichi NPP accident Health Phys 116 (5), 647–656 https:// doi.org/10.1097/hp.0000000000000995 Kurihara, O., Kanai, K., Nakagawa, T., Takada, C., Momose, T., Furuta, S., 2012 Direct measurements of employees involved in the Fukushima Daiichi nuclear power station accident for internal dose estimates: JAEA’s experiences In: Proceedings of the First NIRS Symposium on the Reconstruction of Early Internal Dose in the TEPCO Fukushima Daiichi Nuclear Power Station Accident National Institute of Radiological Sciences, Chiba, Japan NIRS-M-252 :13–25 https://repo.qst.go.jp/?act ion=pages_view_main&active_action=repository_view_main _item_detail&item_id =73765&item_no=1&page_id=13&block_id=21 Likhtarev, I.A., Grulko, G.M., Sobolev, B.G., Kairo, I.A., Pră ohl, G., Roth, P., Henrichs, K., 1995 Evaluation of the 131I thyroid-monitoring measurements performed in Ukraine during May and June of 1986 Health Phys 69 (1), 6–15 https://doi.org/ 10.1097/00004032-199507000-00002 Meisenberg, O., Gerstmann, U.C., 2017 Thyroid monitoring of adults and children after reactor accident with a new dose rate measurement device Radiat Meas 125, 150–153 https://doi.org/10.1016/j.apradiso.2017.04.006 National Institute of Radiological Sciences, 2016 Activity Records of NIRS Employees in Their Responses to the Fukushima Daiichi Nuclear Power Plant Accident NIRS-M286 March 2016 (in Japanese) https://repo.qst.go.jp/?action=reposito ry_uri&item_id=73799&file_id=10& file_no=1 Nishino, S., Tanimura, Y., Yoshitomi, H., Takahashi, M., 2020 Porotype test of a portable thyroid dose monitoring using gamma-ray spectrometers Radiat Meas 134, 106292 https://doi.org/10.1016/j.radmeas.2020.106292 Ohba, T., Ishikawa, T., Nagai, H., Tokonami, S., Hasegawa, A., Suzuki, G., 2020 Reconstruction of residents’ thyroid equivalent doses from internal radionuclides after the Fukushima Daiichi nuclear power station accident Sci Rep 10, 3639 https://doi.org/10.1038/s41598-020-60453-0 Ulanovsky, A.V., Eckerman, K.F., 1998 Modification to the ORNL phantom series in simulation of the responses to thyroid detectors Radiat Protect Dosim 79 (1− 4), 429–431 https://doi.org/10.1093/oxfordjournals.rpd.a032443 Ulanovsky, A.V., Minenko, V.F., Korneev, S.V., 1997 Influence of measurement geometry on the estimate of 131I activity in the thyroid: Monte Carlo simulation of a detector and a phantom Heath Phys 72 (1), 34–41 https://doi.org/10.1097/ 00004032-199701000-00004 Werner, C.J (Ed.), 2017 MCNP User’s Manual LA-UR-17-29981 https://mcnp.lanl.gov /pdf_files/la-ur-17-29981.pdf Yajima, K., Kim, E., Tani, K., Kurihara, O., 2020 A new thyroid monitor using multiple high resolution Gd3(Al, Ga)5O12(Ce) detectors for direct thyroid measurements of small children following a nuclear accident Radiat Meas 133, 106272 https://doi org/10.1016/j.radmeas.2020.106272 Youngman, M.J., 2013 Practical Guidance on Thyroid Monitoring for Radioiodine Using Hand-Held Instruments Health Protection Agency HPA-CRCE-044 https://assets publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/f ile/337139/HPA-CRCE-044_for_website.pdf ... F., Vaz, P., Vrba, T., Vu, I., Youngman, M., Zagyvai, P., 2019 Child and adult thyroid monitoring after a reactor accident (CAThyMARA): technical recommendations and remaining gaps Radiat Meas... direct thyroid measurements of young children following a major nuclear accident Funding This work was financially supported by the Nuclear Regulation Au thority of Japan under the Radiation Safety... Yajima et al Radiation Measurements 150 (2022) 106683 future Summary We developed a new hand-held type thyroid monitor to measure radioiodine in the human thyroid in the case of a major nuclear