Microdosimetry of radon progeny alpha particles in bronchial airway bifurcations

A Monte Carlo code, initially developed for the calculation of microdosimetric spectra for alpha particles in cylindrical airways, has been extended to allow the computation of microdosimetric parameters for multiple source - target configurations in bronchial airway bifurcations. The objective of the present study was to investigate the effects of uniform and non-uniform radon progeny surface activity distributions in symmetric and asymmetric bronchial airway bifurcations on absorbed dose, hit frequency, lineal energy, single hit specific energy and LET spectra. In order to assess the effects of multiple hits, dose-dependent specific energy spectra were calculated by solving the compound Poisson process by iterative convolution. While the simulations showed significant differences of cellular dose quantities at different cell locations for uniformly distributed surface activities, even higher variations, as high as several orders of magnitude, were observed for non-uniform surface activity distributions, depending on the location of the cell and the local activity distribution. © 2005 Oxford University Press

Microdosimetry of inhomogeneous radon progeny distributions in bronchial airways

A Monte Carlo code, initially developed for the calculation of microdosimetric spectra for alpha particles in cylindrical airways, has been extended to allow the computation (i) of additional microdosimetric parameters and (ii) for realistic exposure conditions in human bronchial airways with respect to surface activity distribution and airway geometry. The objective of the present study was to investigate the effects of non-uniform distributions of radon progeny activities in bronchial airways on cellular energy deposition parameters. Significant variations of hit frequencies, doses and microscopic energy deposition patterns were observed for epithelial cell nuclei, depending strongly on the assumed activity distributions. Thus, epithelial cells located at different positions in a given bronchial airway may experience a wide range of biological responses. The results obtained suggest that the hit frequency may be the primary physical parameter for alpha particles, supplemented by microdosimetric single event spectra, to be related to biological effects for chronic low level exposures. © The Author 2005. Published by Oxford University Press. All rights reserved

Lung cancer risk in humans and rats: single vs. multiple exposures

At the cellular level, extrapolation of lung cancer risk from high occupational to low domestic exposures to radon progeny is equivalent to the extrapolation of the carcinogenic effects of multiple to single cellular hits. In the present study, the frequency of multiple cellular hits, their microdosimetric representation in terms of specific energy distributions, and their resulting transformation frequencies were compared to the corresponding effects produced by single hits. To relate these results to realistic inhalation conditions, steady-state 218Po and 214Po surface activities were computed for defined exposure conditions, normalized to a cumulative exposure of 1 Working Level Month (WLM). Cellular hit frequencies for 218Po and 214Po alpha particles to basal and secretory cells were computed for selected bronchial airway generations in human and rat lungs, considering the distribution of target cells in bronchial epithelium. Using analytical and Monte Carlo methods, distributions of specific energy in both target cells were calculated for the traversal of 0, 1, 2, or more alpha particles

Current developments at IRSN on computational tools dedicated to assessing doses for both internal and external exposure

The paper presents the OEDIPE (French acronym that stands for tool for personalised internal dose assessment) and SESAME (for simulation of external source accident with medical images) computational tools, dedicated to internal and external dose assessment, respectively, and currently being developed at the Institute for Radiological Protection and Nuclear Safety. The originality of OEDIPE and SESAME, by using voxel phantoms in association with Monte Carlo codes, lies in their ability to construct personalised voxel phantoms from medical images and automatically generate the Monte Carlo input file and visualise the expected results. OEDIPE simulates in vivo measurements to improve their calibration, and calculates the dose distribution taking both internal contamination and internal radiotherapy cases into account. SESAME enables radiological overexposure doses to be reconstructed, as also victim, source and accident environment modelling. The paper presents the principles on which these tools function and an overview of specificities and results linked to their fields of application. © The Author 2005. Published by Oxford University Press. All rights reserved

SESAME: A software tool for the numerical dosimetric reconstruction of radiological accidents involving external sources and its application to the accident in Chile in December 2005

Estimating the dose distribution in a victim's body is a relevant indicator in assessing biological damage from exposure in the event of a radiological accident caused by an external source. This dose distribution can be assessed by physical dosimetric reconstruction methods. Physical dosimetric reconstruction can be achieved using experimental or numerical techniques. This article presents the laboratory-developed SESAME-Simulation of External Source Accident with MEdical images-tool specific to dosimetric reconstruction of radiological accidents through numerical simulations which combine voxel geometry and the radiation-material interaction MCNP(X) Monte Carlo computer code. The experimental validation of the tool using a photon field and its application to a radiological accident in Chile in December 2005 are also described. © 2009 Health Physics Society

Validation par la mesure d’ŒDIPE, outil d’évaluation de la dose interne personnalisée

La radiothérapie interne ou vectorisée consiste à injecter aux patients des radiopharmaceutiques afin de délivrer des doses de rayonnements aux tumeurs ou organes ciblés. La réalisation d’études dosimétriques est nécessaire pour chaque patient traité par radiothérapie vectorisée ainsi que pour les sujets contaminés par inhalation, blessure ou ingestion. Afin d’atteindre la précision requise dans de tels cas, nous avons développé une méthode dosimétrique, basée sur le code Monte-Carlo de transport des particules MCNPX. L’anatomie de chaque patient ou sujet contaminé est prise en compte sous forme d’une géométrie voxélisée créée à partir d’images tomodensitométriques (CT) ou de résonance magnétique (IRM). Cet outil baptisé ŒDIPE (acronyme d’outil d’évaluation de la dose interne personnalisée) permet de réaliser des études dosimétriques à l’échelle des organes et du voxel. La validation d’un tel outil est complexe car les sources de variations du calcul dosimétrique sont multiples : méthodes de calcul, définitions et représentativité de la géométrie. L’étude présentée ici a pour but de valider l’outil ŒDIPE par comparaison de ses résultats avec des mesures expérimentales obtenues à l’aide de fils thermoluminescents. La comparaison des doses moyennes calculées et mesurées est satisfaisante. Cependant, la mesure et le calcul des distributions spatiales de dose le long des fils thermoluminescents, bien qu’ayant des allures comparables, présentent des écarts significatifs. Cela est dû au fait qu’il est impossible de faire correspondre exactement une portion de fil à un voxel donné

General guidelines for the assessment of internal dose from monitoring data (project IDEAS) [Guide pratique pour estimer la dose interne à partir des résultats de mesure de surveillance (projet IDEAS)]

In recent major international intercomparison exercises on intake and internal dose assessments from monitoring data, the results calculated by different participants varied significantly. This was mainly due to the broad variety of methods and assumptions applied in the assessment procedure. Based on these experiences the need for harmonisation of the procedures has been formulated within an EU research project under the 5th Framework Programme. The aim of the project, IDEAS, is to develop general guidelines for standardising assessments of intakes and internal doses. The IDEAS project started in October 2001 and will end in March 2005. Eight institutions from seven European countries are participating. Inputs from internal dosimetry professionals from across Europe are also being used to ensure a broad consensus in the outcome of the project. The IDEAS project is closely related to some goals of the work of committee 2 of the ICRP and since 2003 there has been close cooperation between the two groups. To ensure that the guidelines are applicable to a wide range of practical situations, the first step has been to compile a database of well-documented cases of internal contamination. In parallel, an improved version of an existing software package has been developed and distributed to the partners for further use. A large number of cases from the database have been evaluated independently by partners in the project using the same software and the results have been reviewed. Based on these evaluations, guidelines are being drafted and will be discussed with dosimetry professionals from around the world by means of a virtual workshop on the Internet early in 2004. The guidelines will be revised and refined on the basis of the experiences and discussions of this virtual workshop and the outcome of an intercomparison exercise organised as part of the project. This will be open to all internal dosimetry professionals. © 2005 EDP Sciences

Comparison of Calculated Spectra for the Interaction of Photons in a Liquid Scintillator: Example of 54Mn 835 keV Emission

The CIEMAT/NIST and TDCR methods in liquid scintillation counting, initially developed for the activity standardization of pure-beta radionuclides, have been extended to the standardization of electron-capture and beta-gamma radionuclides. Both methods require the calculation of the energy spectrum absorbed by the liquid scintillator. For radionuclides emitting X-rays or gamma-rays, when the energy is greater than a few tens keV the Compton interaction is important and the absorption is not total. In this case, the spectrum absorbed by the scintillator must be calculated using analytical or stochastic models. An illustration of this problem is the standardization of 54Mn which is a radionuclide decaying through electron capture. The gamma transition, very weakly converted, leads to the emission of a 835 keV photon. The calculation of the detection efficiency of this radionuclide requires the calculation of the energy spectrum transferred to the scintillator after the absorption of the gamma ray and the associated probability of absorption. The validity of the method is thus dependent on the correct calculation of the energy transferred to the scintillator.JRC.D.4-Isotope measurement