The single-particle microbeam facility at CEA-Saclay
Introduction
MeV-ion microbeams are nowadays frequently used to probe local cell responses to charged particle irradiations as they offer many advantages such as: (i) a full control of the impact points, thus permitting to target individual cells, and in certain cases discriminate cell compartments; (ii) a well-controlled dose delivery, as ion flux is generally monitored in real time and (iii) the possibility of revisiting the experiment as irradiation pattern is stored and one can study separately irradiated cells from un-irradiated cells. Combined with the constant progresses of cellular imaging, mainly based on fluorescence techniques, allowing the probing of chemical specie fluxes, microbeam irradiation facilities are a tool of choice for radiobiologists to investigate detailed responses to ionizing radiations. Consequently, geometry-dependent irradiation effects such as bystander effects are actively studied [1], [2], [3].
An essential condition to ensure a well-controlled experiment, relevant results, and a high credibility from the biologist community is to offer an environment as close as possible to standard biology experiments, as it was pointed out by Folkard et al. [4].
At Saclay, we have developed a microbeam irradiation facility that aims to reach this goal. The key parameters are: (1) a vertical irradiation direction, from bottom to top, in order to maintain the cell cultures horizontally, (2) a standard microenvironment around the cell cultures during irradiation, avoiding any drying process or medium acidification and (3) an original way for scanning the desired irradiation pattern, similar to beam deflection scanning, although with a microbeam being produced using a collimator.
Consequently, encapsulating arrangements are not required and it is possible to perform long term experiments and in situ observations. Mechanical stress induced by acceleration–deceleration cycles when fast mechanical stages are employed is also limited.
The paper gives an overview of the setup, its performances, and presents some results already obtained regarding DNA damage and Reactive Oxygen Species (ROS) signaling induced in targeted and non-targeted cell populations.
Section snippets
Microbeam production
The irradiation end-station is integrated as a part of the Nuclear Microprobe at Saclay. The facility, based on a 3.75 MeV Van de Graaff accelerator is mainly used for elemental analysis in material science [5], geology [6] and toxicology [7]. It is equipped with two horizontal microbeam lines, one of two dedicated to highly radioactive sample microanalysis, as the reaction chamber is located in a specifically designed hot cell, ensuring a complete protection of the experimenters and operators
Irradiation end-station
The main goal of the project, conducting radiobiological researches using microbeams in an environment as close as possible to cellular biology conditions, has had strong consequences on the adopted technological choices regarding the irradiation en-station design. Beyond the vertical horizontal irradiation direction, which obviously is a prerequisite, a number of additional and original features characterize the end-station.
First, culture dishes are based on standard 50 mm-diameter Polystyrene
Cell responses to irradiation related studies
The facility has been already used to conduct experimental studies related to the local response following controlled irradiations [12]. In the frame of toxicity studies, an emphasis was given to uranium, a well-known chemical toxic that is known to fix in bones for long periods and consequently can be considered as a low dose alpha source. The MC3T3 cell line used here originates from osteoblast primary cells.
Summary
A new experimental cell irradiation setup has been developed as an extension to Saclay nuclear microprobe. The project guideline was to develop an irradiation setup in an environment as close as possible to standard cellular biology culture conditions. Cells are irradiated in a vertical direction, are cultured in standard dishes and are maintained with standard temperature and atmosphere conditions in the irradiation setup. To overcome the fact that the microbeam is produced using a collimator,
Acknowledgments
Authors are grateful to Y.P. Kilisky and F. Pontiggia for their technical assistance during radiobiology experiments. We also thank D. Guillier and F. Saillant for accelerator operation.
This project was partially supported by Conseil Général de l’Essonne under Contract ASTRE 2004 “Dispositif d’irradiation ion par ion de cellules et tissus”.
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