Monte Carlo dosimetry for targeted irradiation of individual cells using a microbeam facility.

Microbeam facilities provide a unique opportunity to investigate the effects of ionising radiation on living biological cells with a precise control of the delivered dose. This paper describes dosimetry calculations performed at the single-cell level in the microbeam irradiation facility available at the Centre d'Etudes Nucléaires de Bordeaux-Gradignan in France, using the object-oriented Geant4 Monte Carlo simulation toolkit. The cell geometry model is based on high-resolution three-dimensional voxelised phantoms of a human keratinocyte (HaCaT) cell line. Such phantoms are built from confocal microscopy imaging and from ion beam chemical elemental analysis. Results are presented for single-cell irradiation with 3 MeV incident alpha particles.

A comparison of cellular irradiation techniques with alpha particles using the Geant4 Monte Carlo simulation toolkit.

A comparison of three cellular irradiation techniques using the Monte Carlo simulation toolkit Geant4 is presented in this paper. They involve electrodeposited source of alpha particle-emitting radionuclides, random classical alpha beam irradiation and single cell targeted irradiation using a focused alpha microbeam line. The simulation allows the calculation of hit distributions among the cellular population as well as the absorbed dose for two typical cellular geometries.

Monte-Carlo dosimetry on a realistic cell monolayer geometry exposed to alpha particles.

The energy and specific energy absorbed in the main cell compartments (nucleus and cytoplasm) in typical radiobiology experiments are usually estimated by calculations as they are not accessible for a direct measurement. In most of the work, the cell geometry is modelled using the combination of simple mathematical volumes. We propose a method based on high resolution confocal imaging and ion beam analysis (IBA) in order to import realistic cell nuclei geometries in Monte-Carlo simulations and thus take into account the variety of different geometries encountered in a typical cell population. Seventy-six cell nuclei have been imaged using confocal microscopy and their chemical composition has been measured using IBA. A cellular phantom was created from these data using the ImageJ image analysis software and imported in the Geant4 Monte-Carlo simulation toolkit. Total energy and specific energy distributions in the 76 cell nuclei have been calculated for two types of irradiation protocols: a 3 MeV alpha particle microbeam used for targeted irradiation and a ²³9Pu alpha source used for large angle random irradiation. Qualitative images of the energy deposited along the particle tracks have been produced and show good agreement with images of DNA double strand break signalling proteins obtained experimentally. The methodology presented in this paper provides microdosimetric quantities calculated from realistic cellular volumes. It is based on open-source oriented software that is publicly available.

Imaging physicochemical reactions occurring at the pore surface in binary bioactive glass foams by micro ion beam analysis.

In this work, the physicochemical reactions occurring at the surface of bioactive sol-gel derived 3D glass scaffolds via a complete PIXE characterization were studied. 3D glass foams in the SiO(2)-CaO system were prepared by sol-gel route. Samples of glass scaffolds were soaked in biological fluids for periods up to 2 days. The surface changes were characterized using particle induced X-ray emission (PIXE) associated to Rutherford backscattering spectroscopy (RBS), which are efficient methods to perform quantitative chemical maps. Elemental maps of major and trace elements at the glass/biological fluids interface were obtained at the micrometer scale for every interaction time. Results revealed interconnected macropores and physicochemical reactions occurring at the surface of pores. The micro-PIXE-RBS characterization of the pores/biological fluids interface shows the glass dissolution and the rapid formation of a Ca rich layer with the presence of phosphorus that came from biological fluids. After 2 days, a calcium phosphate-rich layer containing magnesium is formed at the surface of the glass scaffolds. We demonstrate that quantities of phosphorus provided only by the biological medium have a significant impact on the development and the formation of the phosphocalcic layer.

Elemental maps in human allantochorial placental vessels cells. 4. Isoproterenol and sodium nitroprusside effects.

The ionic channels (particularly, K+ and Ca2+ channels) regulate, via the membrane potential, the ionic distribution into the vascular cells. Micro-particule induced X-ray emission (PIXE) analysis was applied to determine the ionic composition of vascular smooth muscle cells (VSMCs) and of vascular endothelial cells (VECs) in the placental human allantochorial vessels in a physiological medium (Hanks' solution) modified by the addition of a NO donor (sodium nitroprusside, SNP) and of a beta-adrenergic stimulator (isoproterenol, ISO). The addition of SNP or ISO induced no modification of the Na, K, Cl, P, S, Mg and Ca concentrations in VSMCs. In VECs, a same effect was observed except an increase of the Mg concentration with ISO. Theses results indicated a retroactive control (active feedback) of the internal ionic distribution by endothelial factors, ionic channels and exchangers.

Elemental maps in human allantochorial placental vessels cells. 3. 5-hydroxytryptamine effects.

The membrane potential, a regulator of vascular tone, is a function of the physiological activities of ionic channels (particularly, K+ and Ca2+ channels in these cells). These channels regulate the ionic distribution into these cells. Micro-particule induced X-ray emission (PIXE) analysis was applied to determine the ionic composition of vascular smooth muscle cells (VSMCs) and of vascular endothelial cells (VECs) in the placental human allantochorial vessels in a physiological medium (Hanks'solution) modified by the addition of a chemical stimulus: 5-hydroxytryptamine (5-HT), an activator of the voltage-sensitive Ca2+ channels. In VSMCs (media layer), the addition of 5-HT induced no modification of the Na, K, Cl, P, S and Ca concentrations but increased Mg concentration. In endothelium (VECs) 5-HT addition implicated an increase of the K, S, Ca concentrations, the concentration of the other ions remained constant. In VECs, Ca and K increase is due to open of L-type voltage-dependent Ca2+ channels and of K(Ca) channels. 5-HT induces also a secretion of endothelium hyperpolarizing factors which implicate decrease of [Ca2+]i in VSMCs opposite to a direct increase by 5-HT. Increase in [Mg2+]i may be due to activation of the Ca/Mg exchanger.