Does the Number of Irradiated Cells Influence the Spatial Distribution of Bystander Effects?

There is growing evidence that the radiation effects at low doses are not adequately described by a simple linear extrapolation from high doses, due, among others, to bystander effects. Though several studies have been published on this topic, the explanation of the mechanisms describing the bystander effects remains unclear. This study aims at understanding how the bystander signals are or can be propagated in the cell culture, namely if the number of irradiated cells influences the bystander response. An A549 cell line was exposed to several doses of α-particles, being the bystander response quantified in two non-irradiated areas. The radius of irradiated areas differs by a factor of 2, and the non-irradiated areas were optimally designed to have the same number of cells. Our results show evidence for bystander effects occurring in cells far away from the irradiated ones, meaning that bystander signals can easily spread throughout the cell culture. Additionally, our study highlights that the damage caused by radiation on the surrounding of irradiated areas could be different according to the number of irradiated cells, i.e., for the same dose value; the overall cellular damage could be different

Simulation of three-dimensional particle deposition patterns in human lungs and comparison with experimental SPECT data

To further validate a stochastic particle deposition model, three-dimensional deposition patterns predicted by that model were compared with corresponding spatial particle deposition data obtained from SPECT measurements. In the in vivo inhalation experiments, two different polydisperse aerosols with mass median aerodynamic diameters of 1.6 ? m and 6.8 ? m were inhaled by 12 test subjects, using different nebulizers. Predicted and measured deposition data were compared on three different levels: (1) total lung deposition, (2) deposition per hemispherical shell, and (3) deposition per airway generation. First, experimental and theoretical total lung deposition data showed good agreement for both the fine (65 ± 9% vs. 55 ± 21%) and the coarse aerosols (55 ± 8% vs. 46 ± 4%). Second, predicted deposition per hemispherical shell also corresponded well with the experimental data, both exhibiting small deposition fractions in the inner shells and a roughly quadratic increase in the outer shells. Third, fair agreement was observed for the deposition fractions per airway generation, both experimental data and modelling predictions exhibiting relatively small deposition fractions in central bronchial airway generations, followed by a steep increase in the peripheral respiratory airways. While the overall agreement between measured SPECT data and computed deposition fractions demonstrates that SPECT data can indeed be used for model validation, the current spatial resolution of the SPECT method allows only a limited validation of model predictions at the single airway generation level

Eurados coordinated action on research, quality assurance and training of internal dose assessments

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. © The Author 2010. Published by Oxford University Press. All rights reserved

New developments in aerosol dosimetry

Dosimetry provides information linking environmental exposures to sites of deposition, removal from these sites, and translocation of deposited materials. Dosimetry also aids in extrapolating laboratory animal and in vitro data to humans. Recent progress has shed light on: properties of particles in relation to their fates in the body; influence of age, gender, body size, and lung diseases on inhaled particle doses; particle movement to the brain via the olfactory nerves; and particle deposition hot spots in the respiratory tract. Ultrafine size has emerged as an important dosimetric characteristic. Particle count, composition, and surface properties are recognized as potentially important toxicology-related considerations. Differences in body size influence airway sizes, inhaled particle deposition, specific ventilation, and specific doses (e.g. per unit body mass). Related to body size, age, gender, species, and strain are also dosimetric considerations. Diseases, such as chronic obstructive pulmonary disease (COPD) and bronchitis, produce uneven doses within the respiratory tract. Traditional concepts of the translocation and clearance of deposited particles have been challenged. Ultrafine particles can translocate to the brain via olfactory nerves, and from the lung to other organs. The clearance rates of particles from tracheobronchial airways are slowed by respiratory tract infections, but newer evidence implies that slow particle clearance from this region also exists in healthy lungs. Finally, hot spots of particle deposition are seen in hollow models, lung tissue, and dosimetric simulations. Local doses to groups of epithelial cells can be much greater than those to surrounding cells. The new insights challenge dosimetry scientists