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In a nuclear emergency, one of the actions taken for the sake of public is to monitor thyroid exposure to radioiodines. Japan's Nuclear Regulation Authority recently published a report on such monitoring and proposed direct thyroid measurements with conventional NaI(Tl) survey meters (e.g. Hitachi model TCS-172) as a primary screening method. A previous study proposed screening levels (SLs) used in these simplified measurements as the net reading values of the TCS-172 device. Age-specific SLs were derived from a thyroid equivalent dose of 100 mSv due to the inhalation intake of 131I. This study addressed the possible influence of short-lived iodine isotopes other than 131I on the simplified measurements. In preparation for such measurements, the responses of the device for 132I as an ingrowth component from 132Te, 133I, 134I and 135I in the thyroid were evaluated by numerical simulations using age-specific stylized phantoms in addition to those obtained for 131I in the previous study. The radioactivity ratios of the relevant isotopes were taken from the inventory data of the Fukushima Daiichi Nuclear Power Plant. The results were used to predict the net readings of the device when 132Te-132I and 133I as well as 131I were inhaled at 24 or 72 h after the shutdown of a nuclear power plant. In these cases, the signals from 132Te-132I and 133I become undetectable a couple of days after intake, which could lead to underestimations of the thyroid dose. To estimate the thyroid dose accurately from the simplified measurements, it is necessary to identify the exact time of intake after the shutdown and the actual physiochemical property of 132Te that affects the thyroid uptake of 132I., (© The Author(s) 2023. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

To improve calibration methods of in vivo counting, our laboratory has developed a computer tool to model internal contamination and assess in vivo activity and corresponding organ absorbed doses. The aim of the recent work was to define a more realistic source based on biokinetic models. The influence of the biokinetic parameters on the in vivo counting was studied through the simulation of an acute inhalation intake of (241)Am. The tissue distribution of activity predicted by the biokinetic model was visualized. Two equivalent methods for determination of the efficiency related to the total activity distributed in the body were used. The comparison between the efficiency taking the biokinetics into account and the classically estimated efficiency quantifies the influence of the activity distribution in the body and provides conversion factors for correcting the classical efficiency to account for biokinetics.

EURADOS working group on ‘Internal Dosimetry (WG7)’ represents a frame to develop activities in the field of internal exposures as coordinated actions on quality assurance (QA), research and training. The main tasks to carry out are the update of the IDEAS Guidelines as a reference document for the internal dosimetry community, the implementation and QA of new ICRP biokinetic models, the assessment of uncertainties related to internal dosimetry models and their application, the development of physiology-based models for biokinetics of radionuclides, stable isotope studies, biokinetic modelling of diethylene triamine pentaacetic acid decorporation therapy and Monte-Carlo applications to in vivo assessment of intakes. The working group is entirely supported by EURADOS; links are established with institutions such as IAEA, US Transuranium and Uranium Registries (USA) and CEA (France) for joint collaboration actions. [ABSTRACT FROM PUBLISHER]

Although great efforts have been made to improve the physical anthropomorphic phantoms used to calibrate in vivo measurement systems, each of these phantoms represents a single average counting geometry and usually contains a uniform distribution of a radionuclide in the tissue substitute. As a matter of fact, significant corrections must be made to phantom-based calibration factors in order to obtain absolute calibration efficiencies applicable to a given individual. The OEDIPE software has been developed at the Institute for Radiological Protection and Nuclear Safety. It allows the direct and fast construction of a voxel phantom from medical images with a realistic distribution of activity between organs and its conversion into computer files to be used online for Monte Carlo calculations. OEDIPE allows determining and visualizing the variation of activity retention in the segmented organs of the phantom and running MCNPX with these calculated source-organs at different times after intake. The influence of the biokinetics of radionuclides on the in vivo measurement as well as the uncertainty on the estimated activity is quantified by comparing the numerical calibration coefficients obtained by considering realistic and dynamic biokinetic distributions of activity with the counting efficiency commonly obtained from simple, homogeneous, and static activity distributions in organs or in the whole body. As an application, the effect of long-term retention tissues was studied through a case of inhalation of an insoluble compound where the thoracic lymph nodes make a significant contribution to the lung counting efficiency. Future work will concern contamination through other routes of intake, such as a wound, and mixtures of radionuclides. [ABSTRACT FROM AUTHOR]

The CONRAD Project is a Coordinated Network for Radiation Dosimetry funded by the European Commission 6th Framework Programme. The activities developed within CONRAD Work Package 5 ('Coordination of Research on Internal Dosimetry') have contributed to improve the harmonisation and reliability in the assessment of internal doses. The tasks carried out included a study of uncertainties and the refinement of the IDEAS Guidelines associated with the evaluation of doses after intakes of radionuclides. The implementation and quality assurance of new biokinetic models for dose assessment and the first attempt to develop a generic dosimetric model for DTPA therapy are important WP5 achievements. Applications of voxel phantoms and Monte Carlo simulations for the assessment of intakes from in vivo measurements were also considered. A Nuclear Emergency Monitoring Network (EUREMON) has been established for the interpretation of monitoring data after accidental or deliberate releases of radionuclides. Finally, WP5 group has worked on the update of the existing IDEAS bibliographic, internal contamination and case evaluation databases. A summary of CONRAD WP5 objectives and results is presented here. [ABSTRACT FROM AUTHOR]

Although great efforts have been made to improve the physical phantoms used to calibrate in vivo measurement systems, these phantoms represent a single average counting geometry and usually contain a uniform distribution of the radionuclide over the tissue substitute. As a matter of fact, significant corrections must be made to phantom-based calibration factors in order to obtain absolute calibration efficiencies applicable to a given individual. The importance of these corrections is particularly crucial when considering in vivo measurements of low energy photons emitted by radionuclides deposited in the lung such as actinides. Thus, it was desirable to develop a method for calibrating in vivo measurement systems that is more sensitive to these types of variability. Previous works have demonstrated the possibility of such a calibration using the Monte Carlo technique. Our research programme extended such investigations to the reconstruction of numerical anthropomorphic phantoms based on personal physiological data obtained by computed tomography. New procedures based on a new graphical user interface (GUI) for development of computational phantoms for Monte Carlo calculations and data analysis are being developed to take advantage of recent progress in image-processing codes. This paper presents the principal features of this new GUI. Results of calculations and comparison with experimental data are also presented and discussed in this work. [ABSTRACT FROM AUTHOR]

Abstract: In vivo measurements are commonly used to determine the incorporated activity of radionuclides. However, for complex or old contaminations, the assessment of the activity distribution among organs is difficult to obtain from measurements only. A method is suggested to assess the activity of organs; it consists in separating the contribution of each contaminated organ in the experimental counts using organ-specific counting efficiencies. The feasibility of the method was first experimentally investigated using two torso phantoms containing radioactive organs. The first phantom contained two radioactive lungs and the second one two lungs and a liver. In the two cases the activity distribution was obtained using experimental specific efficiencies and the bias when compared with true activity was below 5%. The experiments were reproduced by Monte Carlo calculations in order to test the efficiency of the separation method with calculated organ-specific counting efficiencies instead of experimental ones. For the first experiment, the most contributing organ-specific counting efficiencies were correctly simulated but biases as large as 70% were found for the less contributing ones. Consequently, for one organ the activity was correctly assessed but for the other a 20% underestimate was found. For the second experiment, the calculated efficiencies were in better agreement with experimental values and the maximal difference between the calculated and the reference activity was 11%. The method's limits were investigated using perturbation point sources and considering wrong activity distribution hypothesis. The method gives correct results when the number of contaminated organs is overestimated by the startup hypothesis. The opposite situation can be identified only if more measurements than required by the startup hypothesis are carried out. [Copyright &y& Elsevier]