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EURADOS 241Am skull measurement intercomparison
Abstract
In 2011 a measurement intercomparison was launched by EURADOS WG7, with the objective of providing the participants with the tools to calibrate their detection systems for detection of 241Am in the skull bone, and evaluate the variability due to the used of the different calibration phantoms. Three skull phantoms were used in this intercomparison: the USTUR Case 0102 skull phantom, the BfS skull phantom and the CSR skull phantom. Very good agreement was found between the results of the twelve participating laboratories, with relative deviations of less than 15% for the BfS phantom and less than 17% for the USTUR phantom when measurement efficiency in defined positions was compared. However, the phantoms’ measured absolute 241Am activities showed discrepancies of up to a factor of 3.4. This is mainly due to the physical differences between the standard calibration phantoms used by the participants and those used in this intercomparison exercise.
... Only one simple counting geometry was defined for the measurement using the CSR phantom (at vertical position P 0 ). Measurements using the BfS and BPAM (USTUR) phantoms were performed at different positions P i , i = 1,…, n defined in a protocol ( Nogueira et al. 2015). Recommended detector positions and inclinations for the BfS and USTUR phantoms are summarized in Table 1 and Table 2 Am activity in the three skull phantoms. ...
... Regarding exercise 1, good agreement was found among the results of the 12 participants in task 1 ( Nogueira et al. 2015) using one single high-purity germanium (HPGe) detector, with relative deviations of less than 15% for the BfS phantom and less than 17% for the USTUR phantom when the counting efficiencies in the defined test positions were compared. Note that the germanium detectors used here by the participating in vivo laboratories were fabricated either by ORTEC (Atlanta, Georgia, US) or Canberra (Mirion Technologies, Inc., Meriden, Connecticut, US) with different Pos1 43º Pos3 57º Pos4 0º Pos7 0º Pos12 0º sizes, detection areas, and entrance windows (most of them used windows made of carbon, one used a window made of beryllium, and one used a window made of aluminum). ...
... Therefore, measurement results for the P18 detector were not used in final regression analysis of the data. The 241 Am activities calculated by six participants (task 2; Table 3) using their own calibration factors showed discrepancies of up to a factor of 3.4 ( Nogueira et al. 2015), mainly due to the physical differences between the calibration phantom used by each participant and the phantoms used in this EURADOS intercomparison (activity distribution, skull size and filling, etc.). This is an important outcome that requires further discussion. ...
An international intercomparison was organized by Working Group 7, Internal Dosimetry, of the European Radiation Dosimetry Group in collaboration with Working Group 6, Computational Dosimetry, for measurement and Monte Carlo simulation of Am in three skull phantoms. The main objectives of this combined exercise were (1) comparison of the results of counting efficiency in fixed positions over each head phantom using different germanium detector systems, (2) calculation of the activity of Am in the skulls, (3) comparison of Monte Carlo simulations with measurements (spectrum and counting efficiency), and (4) comparison of phantom performance. This initiative collected knowledge on equipment, detector arrangements, calibration procedures, and phantoms used around the world for in vivo monitoring of Am in exposed persons, as well as on the Monte Carlo skills and tools of participants. Three skull phantoms (BfS, USTUR, and CSR phantoms) were transported from Europe (10 laboratories) to North America (United States and Canada). The BfS skull was fabricated with real human bone artificially labeled with Am. The USTUR skull phantom was made from the United States Transuranium and Uranium Registries whole-body donor (case 0102) who was contaminated due to an occupational intake of Am; one-half of the skull corresponds to real contaminated bone, the other half is real human bone from a noncontaminated person. Finally, the CSR phantom was fabricated as a simple hemisphere of equivalent bone and tissue material. The three phantoms differ in weight, size, and shape, which made them suitable for an efficiency study. Based on their own skull calibration, the participants calculated the activity in the three European Radiation Dosimetry Group head phantoms. The Monte Carlo intercomparison was organized in parallel with the measurement exercise using the voxel representations of the three physical phantoms; there were 16 participants. Three tasks were identified with increasing difficulty: (1) Monte Carlo simulation of the simple CSR hemisphere and the Helmholz Zentrum München high-purity germanium detector for calculating the counting efficiency for the 59.54 keV photons of Am, in established measurement geometry; (2) Monte Carlo simulation of particular measurement geometries using the BfS and USTUR voxel phantoms and the Helmholz Zentrum München high-purity germanium detector detector; and (3) application of Monte Carlo methodology to calculate the calibration factor of each participant for the detector system and counting geometry (single or multidetector arrangement) to be used for monitoring a person in each in vivo facility, using complex skull phantoms. The results of both exercises resulted in the conclusion that none of the three available head phantoms is appropriate as a reference phantom for the calibration of germanium detection systems for measuring Am in exposed adult persons. The main reasons for this are: (1) lack of homogeneous activity distribution in the bone material, or (2) inadequate shape/size for simulating an adult skull. Good agreement was found between Monte Carlo results and measurements, which supports Monte Carlo calibration of body counters as an alternative method when appropriate physical phantoms are not available and the detector and source are well known.
... The calibrations were validated in the frame of an international intercomparison action promoted by the European Radiation Dosimetry Group (EURADOS) and involving several international reference laboratories. More details on the phantoms and on the EURADOS intercomparison can be found in (Nogueira et al 2015). The detector efficiencies were also checked using a 241 Am point source, and the energy calibration was verified using a 152 Eu point source and a 40 K source. ...
... Details of these simulations are given in (Nogueira 2014, Nogueira et al 2015. Briefly, the correction factors for the critical head parameters were calculated using two different voxel phantoms, the USTUR voxel phantom (Vrba 2010) and the head of the Max-06 voxel phantom (Kramer et al 2006). ...
Two people were exposed to and contaminated with (241)Am. In vivo determinations of the incorporated (241)Am were performed using a whole-body counter and two partial-body counters for the skull and lung, respectively. Additionally, urine samples were analysed to estimate the systemic activity removed from the body. To improve the geometry of the skull measurements, an optimised detector configuration was used, a calibration with three physical phantoms of the human head was conducted, and the morphological variability between the individuals was also considered. The results of the measurements indicate that activity is not deposited in the deep tissues, rather in the skin tissues close to the body surface. Unfortunately, the many open questions relating to the actual circumstances during and after the incident make the interpretation of this case difficult if at all possible.
... EURADOS exercise for in vivo measurements of americium in skull EURADOS organised an intercomparison exercise (4) , with the objective of providing the participants with the tools to calibrate their in vivo detection system for the measurement of 241 Am in skull (5) and to evaluate the variability in the counting efficiency due to the use of different skull calibration phantoms. Three head phantoms of different sizes and activity distribution, marked with americium in the bone material, were used in this exercise. ...
... Furthermore, with the aim of validating the current skull calibration, CIEMAT WBC participated in the EURADOS intercomparison exercise organised by WG7 'Internal Dosimetry' (4) . This EURADOS action had the objective of providing the participants with the tools to calibrate their in vivo detection system for the measurement of 241 Am in skull and to evaluate the variability in efficiency and sensitivity due to the use of different head calibration phantoms. ...
241Am incorporation due to an incident or chronic exposure causes an internal dose, which can be evaluated from the total activity of this isotope in the skeleton several months after the intake. For this purpose, it is necessary to perform in vivo measurements of this bone-seeker radionuclide in appropriate counting bone geometries with very low attenuation of surrounded tissue and to extrapolate to total activity in the skeleton (ICRP 89, Basic anatomical and physiological data for use in radiological protection: reference values. 2001. 265). The work here presented refers to direct measurements of americium in the Cohen skull phantom at the CIEMAT Whole Body Counter (WBC) using low-energy germanium (LEGe) detectors inside a shielding room. The main goal was to determinate the most adequate head counting geometry for the in vivo detection of americium in the bone. The calibration of the in vivo LEGe system was performed with four detectors with 2 cm of distance to Cohen phantom. Two geometries were meas
... In recent years, comparison exercises and benchmark studies have been organized within the activities of the European Radiation Dosimetry Group EURADOS (Gómez-Ros et al., 2008;Broggio et al., 2012;Vrba et al., 2014;Nogueira et al., 2015;Vrba et al., 2015) on the use of Monte Carlo simulation codes and particular advanced tools to share knowledge, detect difficulties and improve the methods and approaches employed in the field of dosimetry. ...
This work summarises the results of a comparison organized by EURADOS focused on the usage of the ICRP Reference Computational Phantoms. This activity aimed to provide training for the implementation of voxel phantoms in Monte Carlo radiation transport codes and the calculation of the dose equivalent in organs and the effective dose. This particular case describes a scenario of immersion in a 16N beta source distributed in the air of a room with concrete walls where the phantom is located. Seven participants took part in the comparison of results using GEANT4, TRIPOLI-4 and MCNP family codes, and there was detected a general problem when calculating the dose to skeletal tissue and the remainder tissue. After a process of feedback with the participants the errors were corrected and the final results reached an agreement of +/-5%.
... In recent years, comparison exercises and benchmark studies have been organized within the activities of the European Radiation Dosimetry Group EURADOS (Gómez-Ros et al., 2008;Broggio et al., 2012;Vrba et al., 2014Vrba et al., , 2015Nogueira et al., 2015) on the use of Monte Carlo simulation codes and particular advanced tools to share knowledge, detect difficulties and improve the methods and approaches employed in the field of dosimetry. ...
... Radiation Physics and Chemistry 168 (2020) 108514 when available, being designed and fabricated as realistically as possible. Intercomparisons involving in-vivo measurements have been organized by EURADOS together with partners for example from the Lawrence Livermore National Laboratory (LLNL) for thyroid counting (Hickman et al., 2018) and with the United States Transuranium and Uranium Registries (USTUR) for knee and skull counting Nogueira et al., 2015). An alternative to such calibrations using physical phantoms are Monte Carlo (MC) simulations using detector and human-body models (e.g. ...
The European Radiation Dosimetry Group (EURADOS) is a network of organizations and scientists promoting research and development in the dosimetry of ionizing radiation, contributing to harmonization in dosimetry practice across Europe, and offering education and training in areas relevant for dosimetry. As a registered nonprofit association under German law, EURADOS is currently running eight active working groups (WGs): WG2 on “Harmonization of Individual Monitoring”, WG3 on “Environmental Dosimetry”, WG6 on “Computational Dosimetry”, WG7 on “Internal Dosimetry”, WG9 on “Dosimetry in Radiotherapy”, WG10 on “Retrospective Dosimetry”, WG11 on “Dosimetry in High-Energy Radiation Fields”, and WG12 on “Dosimetry in Medical Imaging”. This paper presents recent scientific results obtained within these working groups, and additionally highlights the role of EURADOS as an organization which contributes to the development of a systematic strategy of radiation protection research in Europe.
... Especially significant were the findings with respect to biokinetics, which revealed significant differences from ICRP and the need for revisions in their widely accepted model for americium (Durbin and Schmidt 1985), and the outstanding detailed description of the techniques used for preparation and radiochemical analysis results of the tissues and bones (McInroy et al. 1985). Only half of the skeleton had been analyzed, and the remaining half was used to make in vivo calibration phantoms of head, torso, arm, and leg, which have been made available to other experimenters and used worldwide (Kramer et al. 2011;Nogueira et al. 2015). ...
Dedication: The research of the US Transuranium and
Uranium Registries relies heavily upon postmortem autopsy findings
and radiochemical analysis of tissues. The enormous debt
owed to those now-deceased registrants who unselfishly voluntarily
participated in the US Transuranium and Uranium Registries
program through postmortem donation of their tissues and to
those still-living registrants who have volunteered to be future
postmortem tissue donors is hereby acknowledged with gratitude.
The scientific findings derived from postmortem analysis of these
tissues have been instrumental in advancing our understanding of
the actinide elements in humans and have led to refinement, validation, and confidence in safety standards for those who work
with these elements as well as for the general public. To these generous and anonymous persons who made this ultimate contribution, this paper is dedicated with great thanks and admiration.
Health Phys. 00(00):000–000; 2018
... Collaboration of Working Group 7 and Working Group 6 is traditionally close in terms of the application of MC methods and voxel phantoms for in-vivo calibration of body counters (Task Group 7.4), resulting in a number of intercomparison exercises and publications (Nogueira et al., 2015;Vrba et al., 2015;Breustedt et al., 2016), and on microdosimetric studies of internal emitters (Task Group 7.7), especially for nuclear medicine and radiotherapy applications. Task Group 7.8 is collaborating with Working Group 10 on the application of biodosimetric techniques in scenarios involving accidental internal exposures. ...
Since the early 1980s, the European Radiation Dosimetry Group (EURADOS) has been maintaining a network of institutions interested in the dosimetry of ionising radiation. As of 2017, this network includes more than 70 institutions (research centres, dosimetry services, university institutes, etc.), and the EURADOS database lists more than 500 scientists who contribute to the EURADOS mission, which is to promote research and technical development in dosimetry and its implementation into practice, and to contribute to harmonisation of dosimetry in Europe and its conformance with international practices. The EURADOS working programme is organised into eight working groups dealing with environmental, computational, internal, and retrospective dosimetry; dosimetry in medical imaging; dosimetry in radiotherapy; dosimetry in high-energy radiation fields; and harmonisation of individual monitoring. Results are published as freely available EURADOS reports and in the peer-reviewed scientific literature. Moreover, EURADOS organises winter schools and training courses on various aspects relevant for radiation dosimetry, and formulates the strategic research needs in dosimetry important for Europe. This paper gives an overview on the most important EURADOS activities. More details can be found at www.eurados.org.
... The PopTop capsule is closed with a window made of carbon -epoxy composite. This type of the detector is no longer on sale; however, this detector or similar ones are used for in vivo partial-body measurements to assess actinides activity in the human body (4,5) . The created model with annotations to the dimensions and construction is shown in Figure 1. ...
Mathematical calibration is an increasingly popular technique among laboratories with a whole- or partial-body counters. A
mathematical calibration employing a voxel phantom and Monte Carlo radiation transport code simulations has many benefits
and can overcome many limitations of detector efficiency calibration using physical anthropomorphic phantoms. This publication
tries to identify key factors for detector modelling. The influence of such parameters depends on energy and thus is studied
in the gamma energy range of detectable radionuclides, i.e. from 15 keV to 1.5 MeV.
This work summarises the results of a comparison organized by EURADOS focused on the usage of the ICRP Reference Computational Phantoms. This activity aimed to provide training for the implementation of voxel phantoms in Monte Carlo radiation transport codes and the calculation of the dose equivalent in organs and the effective dose. This particular case describes a scenario of immersion in a¹⁶N beta source distributed in the air of a room with concrete walls where the phantom is located. Seven participants took part in the comparison of results using GEANT4, TRIPOLI-4 and MCNP family codes, and there was detected a general problem when calculating the dose to skeletal tissue and the remainder tissue. After a process of feedback with the participants the errors were corrected and the final results reached an agreement of ±5%.
Incorporation of bone seeking alpha-emitting radionuclides such as 241Am are of special concern, due to the potential of alpha particles to damage the extremely radiation-sensitive bone marrow. In the case of an internal contamination with 241Am, direct in-vivo measurements using Gamma-detectors are typically used to quantify the incorporated activity. Such detectors need to be calibrated with an anatomical phantom, for example of the skull, of known 241Am activity that reproduces the anatomy of the measured individual as closely as possible. Any difference in anatomy and material composition between phantom and individual will bias the estimation of the incorporated activity. Consequently, in this work the impact of the most important anatomical parameters on detection efficiency of one of the germanium detectors of the Helmholtz Center Munich (HMGU) partial body counter were systematically studied. For that a detailed model of the germanium detector was implemented in the Monte Carlo codes GEANT4 and MCNPX. To simulate the detector efficiency, various skull voxel phantoms were used. By changing the phantom dimensions and geometry the impact of parameters such as shape and size of the skull, thickness of tissue covering the skull bone, distribution of 241Am across the scull and within the skull bone matrix, on the detector efficiency was studied. Approaches to correct for these parameters were specifically developed for three physical skull phantoms for which Voxel phantoms were available: Case 102 USTUR phantom, Max-06 phantom, BfS phantom. Based on the impact of each parameter, correction factors for an "individual-specific" calibration were calculated and applied to a real 241Am contamination case reported in 2014. It was found that the incorporated 241Am activity measured with the HMGU partial body counter was about twice as large as that estimated when using the BfS skull phantom without applying any correction factor for person-specific parameters. It is concluded that the approach developed in the present study should in the future be applied routinely for skull phantom measurements, because it allows for a considerably improved reconstruction of incorporated 241Am using partial body counters.
Après l’incorporation de radionucléides dans l’organisme, l’imagerie quantitative en médecine nucléaire et l’anthroporadiométrie sont utilisés pour quantifier l’activité retenue. L’étalonnage de ces systèmes in vivo peut être amélioré afin de tenir en compte de la variabilité individuelle. En vue d’optimiser la mesure de l’activité retenue, des fantômes d’étalonnage innovants ont été réalisés par impression 3D. L’infographie 3D a été utilisée pour la conception, en parallèle avec un travail d’ingénierie permettant l’inclusion de radionucléides et l’adaptation aux besoins des utilisateurs. Un jeu de fantômes thyroïdiens adapté à l’âge a été développé et utilisé pour améliorer la mesure anthroporadiométrique thyroïdienne des enfants. À la suite d’une étude systématique, les coefficients d’étalonnage des installations de routine et de crise de l’IRSN ont été déterminés pour l’adulte et les enfants de 5, 10 et 15 ans. Un fantôme thyroïdien pathologique a été développé en plus du jeu de fantômes thyroïdiens dédié à la crise pour améliorer la mesure de fixation thyroïdienne en médecine nucléaire. Une étude multicentrique a été réalisée pour optimiser l’étalonnage afin de mieux personnaliser le traitement des pathologies bénignes de la thyroïde. Pour l’anthroporadiométrie pulmonaire, une famille de fantômes de poitrine a été développée pour améliorer la surveillance des travailleuses du nucléaire. Finalement, ce travail de recherche a permis de développer des fantômes adaptés aux besoins et de démontrer leur utilité pour la quantification de l’activité en dosimétrie interne.
Dose assessment after intakes of radionuclides requires application of biokinetic and dosimetric models and assumptions about
factors influencing the final result. In 2006, a document giving guidance for such assessment was published, commonly referred
to as the IDEAS Guidelines. Following its publication, a working group within the European networks CONRAD and EURADOS was
established to improve and update the IDEAS Guidelines. This work resulted in Version 2 of the IDEAS Guidelines, which was
published in 2013 in the form of a EURADOS report. The general structure of the original document was maintained; however,
new procedures were included, e.g. the direct dose assessment method for 3H or special procedure for wound cases applying the NCRP wound model. In addition, information was updated and expanded, e.g.
data on dietary excretion of U, Th, Ra and Po for urine and faeces or typical and achievable values for detection limits for
different bioassay measurement techniques.
A simple hemispherical phantom has been designed and prepared for the EURADOS intercomparison exercise on 241Am activity determination in the skull (2011–13). The phantom consists of three parts that substitute bone and soft tissues.
241Am is deposited on the surfaces of the bone-substituting part. The design and assumed composition of phantom parts are discussed.
A preparation of the voxel representation of the phantom is described. The spectrum of a real measurement of the physical
phantom agrees well with the simulation. The physical phantom, and its voxel representation, is provided to the participants
of the intercomparison exercise.
The United States Transuranium and Uranium Registries are unique human tissue research programs studying the distribution, dose, and possible biological effects of the actinide elements in man, with the primary goal of assuring the adequacy of radiation protection standards for these radionuclides. The Registries research is based on radiochemical analysis of tissues collected at autopsy from voluntary donors who have documented occupational exposure to the actinides. To date, tissues, or in some cases radioanalytical results only, have been obtained from approximately 300 individuals; another 464 living individuals have volunteered to participate in the Registries research programs and have signed premortem informed consent and autopsy permissions. The Registries originated at the National Plutonium Registry which was started in 1968 as a then Atomic Energy Commission project under the aegis of a prime contractor at the Hanford site. In 1970, the name was changed to the United States Transuranium Registry to reflect a broader involvement with the higher actinides. In 1978, an administratively separate parallel registry, the United States Uranium Registry, was formed to carry out similar studies among uranium fuel cycle workers.
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.
A voxel phantom has been developed to simulate in vivo measurement systems for calibration purposes. The calibration method presented here employs a mathematical phantom, produced in the form of volume elements (voxels), obtained through magnetic resonance images of the human body. The voxel phantom has a format of 871 'slices' each of 277 x 148 picture elements. The calibration method uses the Monte Carlo technique to simulate the tissue contamination, to transport the photons through the tissues and to simulate the detection of the radiation. The program was applied to obtain calibration factors for the in vivo measurement of 241Am deposited on the cortical bone surface of a real contamination case, and to the simulation of in vivo measurements of 241Am deposited on the cortical bone surface of three head phantoms, as measured with a germanium detector. The calculated and real activities in all four cases were found to be in good agreement. The results indicate that mathematical phantoms could eventually substitute for physical phantoms in the calibration of in vivo measurements for low energy radionuclides.
241Am is known to be a bone-seeking isotope. In the long term it enters the human skeleton. In this paper, the case of a now 62 year old male subject who incorporated 241Am in the early seventies, is used in order to compare state-of-the-art techniques for the detection of 241Am in the human skeleton. The individual was measured using either partial (4 laboratories) or whole-body counters (1 laboratory). The results of each laboratory are discussed separately. The skull measurements, performed by four laboratories, are in good agreement when using the same skull calibration phantom. Based on these results, the estimated total skeleton activity is in reasonable agreement with the result of a whole-body measurement performed by the fifth laboratory. A preliminary 241Am skeleton burden of about 3.5 kBq is estimated for 1996.
The International Commission on Radiological Protection (ICRP) is currently preparing new recommendations which will replace those released in ICRP 1991, 1990 Recommendations of the ICRP ICRP Publication 60 (Oxford: Pergamon). The draft report previews a change for the effective dose with respect to the number of organs and tissues to be included in its calculation. In the future, adipose tissue, connective tissue, the extrathoracic airways, the gall bladder, the heart wall, the lymphatic nodes, the prostate and the salivary glands have to be taken into account for the determination of the effective dose. This study reports on a second segmentation of the recently introduced male adult voxel (MAX) and female adult voxel (FAX) phantoms with regard to the new organs and tissues, but also presents a revised representation of the skeletons, which had not been adjusted to ICRP-based volumes in the first release of the two phantoms.
The in vivo measurement of the activity deposited in the skeleton is a very useful source of information on human internal contaminations with transuranic elements, e.g. americium 241, especially for long time periods after intake. Measurements are performed on the skull or the larger joints such as the knee or elbow. The paper deals with the construction of an anthropomorphic numerical phantom based on CT scans, its potential for calibration and the estimation of the uncertainties of the detection system. The density of bones, activity distribution and position of the detectors were changed in individual simulations in order to estimate their effects on the result of the measurement. The results from simulations with the numerical phantom were compared with the results of physical phantoms.
A new anthropometric phantom has been developed for use in calibrating in vivo measurements of bone-seeking radionuclides. The phantom has the external shape and appearance of the human adult knee and contains a realistic femur, patella, tibia, and fibula. Unique formulations of polyurethanes, CaCO3, and other trace materials are used in construction of the phantom to produce substitutes for human tissue having the same density, attenuation coefficient, and effective Z as that of human muscle and trabecular bone. The formulation for trabecular bone includes provision for a precisely known quantity of radioactive material that is either uniformly distributed throughout the bone matrix or deposited on the exterior surface. The knee phantom is assembled in three interlocking sections that simplify inserting the skeletal structures and prevent streaming. One or more detectors can easily be positioned on the top or sides of the phantom. Intercomparison measurements of 241Am in bone using separate arrays of phoswich and germanium detectors demonstrate that a single knee phantom exhibits the same detection efficiency as that using the skull. In vivo measurement of the knee is a desirable alternative to the head if facial contamination is present or when evaluating recent exposure to bone seeking radionuclides, since bones of the knee exhibit more rapid uptake than the skull. In practice, greater measurement efficiency can be obtained by placing detectors over both knees since a larger fraction of the total body activity is observed. Calibration measurements using the new anthropometric knee phantom demonstrate that it is durable, easy to use, and provides consistent results over repeated measurements.
An analysis and evaluation of 241Am in the whole body of a donor to the U.S. Transuranium Registry (USTR) is presented in five parts. The USTR donor's pertinent medical history, autopsy findings and antemortem evaluations of intake and systemic burden are described in Parts I and II. The donor was a 49-yr-old male Caucasian radiochcmist who died of metastic melanoma in 1979. His work with actinide elcments began in 1952, and the greatest potential for intake of 241Am was when he used an unsealed 241Am source in his doctoral research (1952-54). The first indication that an intake had occurred was the detection of 241Am in a urine sample collected in 1958 as part of an internal dosimetry surveillance program. In-vivo estimates of the initial 241Am intake, based on sporadic urine samples and three sets of external photon measurcments, ranged from 0.23-1.1 uCi depending on the calculational models and calibration factors used. No chelation therapy was applied. The time of intake was estimated to be approximately 25 yr before death. External photon measurements made on the donor's body and dissected bones, presented in Part III, have yielded new and more accurate calibration factors for external in-vivo measurcment of the 60-keV gamma rays of 241Am and the 13.2- and 14-keV x rays of 239Pu and 238Pu. The symmetrical distribution of 241Am in the bones of the right and left sides of the body and the reliability of total skeletal 241Am estimated from external measurcments of 241Am in the head were confirmed. The soft tissues and about one-half of the skeleton were weighed wet, ashed, reweighed and analyzed radiochemically for 241Am, as described in Part IV. The measured total 241Am in the body was 147.4 nCi, distributed as follows: soft tissues of left hand, 1.9%; liver, 6.3%; respiratory tract tissues, 1.5%; other organs, 0.9%; combined structural soft tissues (muscle, skin, connective tissue), 8.6%; mineralized tissues (bones, teeth}, 80%. The expectations of similar 241Am concentrations in bones of grossly similar structure and also in parts of bones of similar microscopic structure were confirmed. The range of 241Am concentrations in the bones and parts of bones at about 25 yr after the most probable time of intake (79 +- 18 dis/min/g ash in 21 specimens of compact bone to 130 +- 9 dis/min/g ash in 14 specimens of cancellous bone in red marrow) is substantially narrower than is found in the bones of animals shortly after 241Am is administered, suggesting that skeletal concentration approaches uniform concentration at long burden times. About 80% of the skeletal 241Am was in compact bone and cancellous bone in fatty marrow and 20% was in cancellous bone in red marrow. The weights of the bones and the radiochcmical data from the tissues and bones of the USTR donor were used in Part V to develop and evaluate a five-compartment metabolic model for 241Am and to assess the model recommended currently by the International Commission on Radiological Protection (ICRP) (1979). The model includes an implicit, rather than explicit, transfer compartment (plasma) that communicates with urinary excretion and four tissue compartments: liver, which also communicates with fecal excretion through bile; two bone compartments (Bs. which remodels slowly, and BF, which remodels more rapidly); two soft tissue compartments (ST2, which is depleted rapidly, and ST2, a non-returning sink which communicates only with ST2). The bone compartments were defined anatomically: BF consists of skeletal parts that are mainly cancellous bone in red marrow, and Bs, the rest of the skeleton, consists mainly of compact bone and cancellous bone in fatty marrow. The initial distribution of 241Am in the adult male human skeleton was estimated by combining the initial concentrations (activity/g ash) of 241Am in monkey bones and bone parts and the ash weights of the same skeletal parts of the USTR donor. The five distribution fractions, the initial 241Am contents of the five tissue compartments and three of the seven turnover rates needed to solve the model were assigned numerical values based on animal experiments and available human experience. The four unknown rate constants were evaluated with a Numerical Algorithms Group library computer program by requiring the results of the model predictions to match within one percent the observed excretion rates and the tissue distribution of 241Am in the USTR donor at about 25 yr after intake. Numerical solution of the modei equations yielded values for the unknown rate constants with the original intake calculated to be 0.214 [mu]Ci of 241Am. The small fraction of the 241Am body content in the testes of the USTR donor (15 dis/ min) suggests that the current ICRP model of Am metabolism overestimates the genetic risk. The model also predicts a decline in the daily rate of urinary excretion from 8 X 10-5 of the contemporary body content at about six months after intake to 1.5 X 10-5 at about 25 yr and numbers of transformations in 50 yr in the skeleton and liver, respectively, of 1.5 and 0.25 times the values obtained from the current ICRP model. About 75% of the transformations in the skeleton occur in bone compartment Bs, which is mainly compact bone. Most of the Am initially deposited in the skeleton will be recirculated at least once; at about 40 yr after intake, the Am concentration in the skeleton will approach uniformity. Applications of this general model to patterns of intake other than brief exposures, to women and to men of different ages and races, to the modelling of other bone-seeking elements and as a tool in planning and assessment of chelation therapy are discussed. Detailed summaries appear at the end of each section.
(C)1985Health Physics Society
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.
In vivo measurement of actinide activity in the skeleton is a valuable source of information on human internal contamination. Estimates of skeleton activity are based on measurements of the knee, elbow or skull. Different laboratories use different measurement geometries. Different calibration phantoms and detectors are used, making a comparison of detection efficiencies rather difficult. This paper compares various head measurement geometries when using MC simulations with a voxel head phantom.
New York University Medical Center's Institute of Environmental Medicine (NYUMC/IEM) was called upon by representatives of the United States Transuranic Registry to reconstruct a human skull phantom for the purpose of producing a calibration structure to be used for determining 241Am skeletal content from in vivo measurements. The human skull represented a deposition pattern of 241Am in the bone matrix which had accumulated into the bone via natural metabolic processes after an accidental intake. Soon after death, the skull was sagittally divided and the left lateral side was analyzed radiochemically. Assuming symmetry of deposition, and based on measurements of the right lateral side of the skull performed at NYUMC/IEM as well as results of radiochemical analysis of sections of the left side, the activity content of the right side was estimated to be 307 +/- 4 Bq (8.3 +/- 0.1 nCi). The right side was subsequently paired with a blank left lateral of a control skull and embedded into tissue-equivalent material. The reconstructed skull phantom was then evaluated to determine its applicability as a calibration phantom which could be used to estimate skeletal burdens of 241Am.
Los Alamos National Laboratory has analyzed autopsy tissue for the USTR, as a part of its study of the uptake, distribution and retention of Pu and other transuranic elements in occupationally exposed workers since 1978. In April 1979, Los Alamos received the internal organs and bone samples from the first whole-body donation to the USTR. The donor was known to have an internal deposition of 241Am. All soft tissue, the bones from the right half of the skeleton, and the odd-numbered vertebrae were received at Los Alamos in February 1980. The bones were subdivided along anatomical areas of interest. All soft tissues and bone specimens were analyzed for their 241Am content. A total deposition of 147.4 nCi 241Am was measured. Approximately 18% of the 241Am remaining in the body (disregarding that in the left hand), was found in the soft tissues, and 82% was in the bones and teeth. The soft tissues and organs containing the largest amounts of 241Am were the combined soft tissue (striated muscle, connective tissue and skin) 8.8%; liver, 6.4% and respiratory tract, 1.5%. The remaining organs accounted for 0.9% of the systemic burden.
Measurements of (241)Am L X-ray emission probabilities were conducted using both HPGe and Si(Li) detectors. The efficiency calibrations of these detectors were performed by means of a tunable, monochromatic photon beam and the determination of the thickness of absorbing materials inside the detector. These efficiency calibrations were obtained without any reference to radionuclide decay data, and with 0.8% relative standard uncertainty. The complex L X-ray region was processed using Voigt functions and by taking account of the detector response function established with the monochromatic beam. Twenty-two components of the L X-ray group were identified and quantified. The present results are compared with previously published data.
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EURADOS -Internal Dosimetry Network
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