The aim of this study is to provide data that increase knowledge about the possible health effects of exposure to 90Sr contaminant in drinking water. 90Sr detection in the mouse bone model plays an important complementary role with computational dosimetry in these investigations. S-value (absorbed dose per unit cumulated activity) calculations using Monte Carlo (MC) simulations, 90Sr detection by liquid scintillation β counting in the femur bone and X-ray microanalysis were carried out. The present work is focused on using MCNPX and its validation at a cellular level. The cytoplasm (Cy), nucleus (N) and 90Sr radiation source were simulated with the MC code MCNPX. Cells are assumed to be spherical, with the radii of the cell and cell nucleus ranging from 2 to 10 μm. The S-value (in Gy/Bq.s) calculations were provided for a 90Sr source distributed uniformly in the cell nucleus or cytoplasm and for two source-target combinations (t←s). A comparison between the calculated MC results and the MIRD values agreed very well since the relative deviations are less than 4%. The earliest results of X-ray microanalysis indicated that the 90Sr was below the detection limit (<0.1%) in the bone tissue. However, the measurements by liquid scintillation showed the presence of 90Sr in the femur bone.

The knowledge of the absorbed radiation dose is essential in order to interpret the results of animal experiments with chronic ingestion of radionuclides by rodents. In order to evaluate this absorbed dose, we applied the dose conversion factors proposed by ICRP publication 108 to mouse chronic ingestion experiments with 20 kBq.L-1137Cs- or 90Sr-contaminated water. The results indicated that whole-body absorbed doses were 9 mGy and 10 mGy by the end of 20 weeks of 137Cs or 90Sr ingestion, respectively. These results of dose calculations were compared with results obtained with a more refined method using published organ-specific absorbed fractions of energy. There was good agreement between the two methods, indicating that, despite the simple hypotheses used to apply the ICRP 108 dose conversion factors to our mouse model, this method allows one to calculate in a simple and reliable way the absorbed radiation dose received by the rodents during long-term experiments on chronic ingestion of radionuclides.

A workshop dedicated to cancer risks associated with low-dose internal contamination was organised in March 2011, in Paris, in the framework of the DoReMi (Low Dose Research towards Multidisciplinary Integration) European Network of Excellence. The aim was to identify the best epidemiological studies that provide an opportunity to develop a multidisciplinary approach to improve the evaluation of the cancer risk associated with internal contamination. This workshop provided an opportunity for in-depth discussions between researchers working in different fields including (but not limited to) epidemiology, dosimetry, biology and toxicology. Discussions confirmed the importance of research on the health effects of internal contamination. Several existing epidemiological studies provide a real possibility to improve the quantification of cancer risk associated with internal emitters. Areas for future multidisciplinary collaborations were identified, that should allow feasibility studies to be carried out in the near future. The goal of this paper is to present an overview of the presentations and discussions that took place during this workshop.

Le syndrome hématopoïétique induit par une irradiation accidentelle reste difficile à traiter, essentiellement du fait de l’hétérogénéité de l’irradiation. La conséquence est qu’il y a toujours un territoire médullaire partiellement protégé de l’irradiation. Le choix d’une stratégie thérapeutique va dépendre essentiellement de l’évaluation des dommages radio-induits à la moelle osseuse, telle qu’elle peut être faite à partir de différents bio-indicateurs de dose ou de dommages comme le suivi de la concentration sanguine de Flt3 ligand. Les options thérapeutiques restent limitées à la greffe de cellules souches hématopoïétiques ou aux traitements de soutien. Récemment, de nouvelles approches de thérapie cellulaire autologue ont été proposées, et ont apporté un éclairage nouveau sur le syndrome de défaillance multi-viscérale radio-induit. D’autres résultats récents du laboratoire montrent que parmi les choix possibles, la stimulation de l’hématopoïèse résiduelle par l’injection de cytokines telles que le G-CSF reste l’une des options thérapeutiques les plus intéressantes. Ces donnés nouvelles soulignent l’importance de la notion d’hématopoïèse résiduelle, mais aussi le fait que les mécanismes de régulation de l’hématopoïèse résiduelle après irradiation restent mal connus.

Plasma Flt3-ligand as a prognostic bio-indicator of radiation-induced bone marrow damage. Following an accidental irradiation, the choice between different therapeutic strategies mainly depends upon the estimated radiation-induced bone marrow damage. It was shown recently that the serum concentration of Flt3-ligand (FL), a cytokine mainly acting on immature haemopoietic cells, is highly elevated in either acquired or induced bone marrow aplasia. This suggested to us that FL measurement could be used as a bio-indicator of radiation-induced bone marrow damage. In order to verify this hypothesis, studies were conducted in a non human primate model as well as in humans undergoing radio and/or chemotherapy. Results showed that the increase in FL concentration on day 5 after irradiation is predictive of the evolution of the haemopoietic syndrome. Similar results were obtained in humans. Overall these results suggested that FL measurement could be used as a reliable bio-indicator of radiation-induced bone marrow damage in accidental irradiation situations.

Les lymphocytes T sont l'une des populations les plus radiosensibles de l'organisme. La reconstitution des lymphocytes T est lente, et des déficits quantitatifs et qualitatifs apparaissent à long terme chez les personnes irradiées. Les mécanismes de la reconstitution lymphocytaire T sont mal connus, et en particulier le rôle joué par le thymus dans cette reconstitution reste peu clair. Le thymus est l'organe lymphode primaire dans lequel se différencie l'ensemble des populations lymphocytaires T durant la vie foetale et post-natale. Le thymus a été considéré pendant longtemps comme étant inactif à l'age adulte. Cependant, des données récentes montrent que le thymus reste, au moins en partie, fonctionnel à l'age adulte. Ceci suggère un rôle important du thymus dans l'homostasie des populations lymphocytaires T, mais aussi dans la reconstitution des lymphocytes T aprés irradiation, y compris à l'age adulte. Par ailleurs, des études récentes révèlent que les effets des rayonnements ionisants sont, au moins en partie, responsables des déficits quantitatifs des lymphocytes T observés à long terme après irradiation. Ces données montrent la nécessité de poursuivre l'étude des effets des rayonnements ionisants sur le thymus, en particulier par la recherche de bio-indicateurs du fonctionnement du thymus en situation physiologique normale, mais aussi en situation physiopathologique d'irradiation accidentelle.