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.
The paper describes measurement of the linear attenuation coefficients for 59.5 keV, 122.0 keV and 344.5 keV photons and Hounsfield units for 80 kVp and 120 kVp computed tomography imaging of a large ...set of commercially 3D-printed test samples of different plastic materials aiming to provide a basis for a selection of a suitable and available material for 3D printing of medical phantoms used in radiology, and specifically for imaging in targeted radionuclide therapy. The results were compared to ICRU44 skeletal muscle and adipose tissues. The results also showed large differences between photon attenuation properties of the same type of plastic material printed by different companies on different printers using filaments from different manufacturers. As a result, it is highly recommended to print a medical phantom on the same printer, with the same settings, and with the same filament as the test sample.
Potassium iodide (KI) is a well-known thyroid prophylactic agent that blocks the incorporation of radioactive iodide in the thyroid; it is generally available for oral administration by the ...population in case of a nuclear release. However, the blockage provided by KI is not 100% effective and therefore activity could still be measured in the thyroid after an intake of radioactive iodine. As a consequence of KI administration the thyroid retention function and the thyroid dose coefficient are modified. To assess the thyroid dose from in vivo measurements these two quantities must be taken into account.
In this work we considered the inhalation of 131-iodine by adult, children (1, 5, 10 years-old) and adolescents (15 years). The effect of KI administration was modelled by a time-dependent blood to thyroid transfer rate coefficient. The model was benchmarked against dose coefficient in the absence of KI and against the protective effect curves depending on KI administration time.
This KI specific model was used to provide correction factors for dose assessment. These multiplicative correction factors apply to a “classical” dose assessment, i.e. a dose assessment based on the ICRP default model that ignores the KI effect. This solution has been preferred since it provides ready to use values avoiding implementing the KI specific model. The correction factors depend on the measurement time and on the KI administration time. They are relatively independent of age and can be described by simple analytic functions. Working examples are provided in this study.
For examples, KI administration 12h before the intake and early in vivo measurements (between 4h and 64h) after the intake give correction factors between 1.2 and 15. For late measurements the correction factors are generally small. If KI has been taken after the intake the correction factors are also generally small, except for very early measurements.
•Interpretation of thyroid measurement after stable iodine prophylaxis.•Factors are provided to correct the usual interpretation that disregards stable iodine.•The corrections are based on a biokinetic model describing thyroid blockage.•Applies to all ages and inhalation of iodine-131.
The paper deals with the physical skull phantoms Bundesinstitut fuer Strahlenschutz and BPAM-001, which are used in order to calibrate in vivo detection systems for estimation of (241)Am activity in ...the skeleton. Their voxel models were made and used in the Monte Carlo simulations. The results of the simulation were compared with measurements and reasonable agreement was observed. Several aspects such as materials and source distributions used in the models were discussed.
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.
Working Group (WG) 6 'Computational Dosimetry' of the European Radiation Dosimetry Group promotes good practice in the application of computational methods for radiation dosimetry in radiation ...protection and the medical use of ionising radiation. Its cross-sectional activities within the association cover a large range of current topics in radiation dosimetry, including more fundamental studies of radiation effects in complex systems. In addition, WG 6 also performs scientific research and development as well as knowledge transfer activities, such as training courses. Monte Carlo techniques, including the use of anthropomorphic and other numerical phantoms based on voxelised geometrical models, play a strong part in the activities pursued in WG 6. However, other aspects and techniques, such as neutron spectra unfolding, have an important role as well. A number of intercomparison exercises have been carried out in the past to provide information on the accuracy with which computational methods are applied and whether best practice is being followed. Within the exercises that are still ongoing, the focus has changed towards assessing the uncertainty that can be achieved with these computational methods. Furthermore, the future strategy of WG 6 also includes an extension of the scope toward experimental benchmark activities and evaluation of cross-sections and algorithms, with the vision of establishing a gold standard for Monte Carlo methods used in medical and radiobiological applications.
A simple hemispherical phantom has been designed and prepared for the EURADOS intercomparison exercise on (241)Am activity determination in the skull (2011-13). The phantom consists of three parts ...that substitute bone and soft tissues. (241)Am 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 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.
In order to assess the reliability of Monte Carlo (MC)-based numerical calibration of in vivo counting systems the EURADOS network supported a comparison of MC simulation of well-defined experiments. ...This action also provided training for the use of voxel phantoms. In vivo measurements of enriched uranium in a thoracic phantom have been carried out and the needed information to simulate these measurements was distributed to 17 participants. About half of the participants managed to simulate the measured counting efficiency without support from the organisers. Following additional support all participants managed to simulate the counting efficiencies within a typical agreement of ±5% with experiment.
► We perform well-defined in vivo calibration measurements of enriched uranium in lungs. ► A voxel model of the phantom and other needed data are provided to participants. ► Participants perform Monte Carlo simulation of the counting efficiencies. ► For about half of the participants the agreement with experiment is within ±5%. ► Other participants needed support to obtain this agreement.
This communication summarizes the results concerning the Monte Carlo (MC) modelling of Germanium detectors for the measurement of low energy photons arising from the “International comparison on MC ...modelling for in vivo measurement of Americium in a knee phantom” organized within the EU Coordination Action CONRAD (Coordinated Network for Radiation Dosimetry) as a joint initiative of EURADOS working groups 6 (computational dosimetry) and 7 (internal dosimetry). MC simulations proved to be an applicable way to obtain the calibration factor that needs to be used for in vivo measurements.
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