LABORATORI NAZIONALI DI LEGNARO
Ionizing radiation is an essential tool in the therapeutic arsenal of oncology. Recently, radiation therapy has become more complex with the emergence of new technologies derived from particle accelerators, able to perform conformal irradiations with different radiation qualities of high and low linear energy transfer (LET). This technological evolution has brought new benefits to patients but also new risks. Investigating and quantifying the existence of a causal link between the early effects and the late effects in tissues is a key issue for understanding the effects of ionizing radiation on the body. The study, at the micrometric scale, of the relationship between the topology of energy deposition and the initial biological events (mainly signs of cell damage) is the first step in this process. The aim of this study is to evaluate the probability of interaction between the particle and the DNA as a function of radiation quality using the analysis of nuclear foci formation such as γ-H2AX and 53BP1 observed by immunofluorescence. Using the microbeam facility at the Physikalisch-Technische Bundesanstalt (PTB), cultures of primary human cells were exposed to α particles of 3 different energies with respective LETs of 37 keV/µm, 90 keV/µm or 160 keV/µm, or to protons with a LET of 23 keV/µm. Thirty minutes after irradiations, the cells were fixed and the immunofluorescence protocol was followed. The foci analysis is based on a platform of high-throughput microscopy including a powerful and robust infrastructure necessary for a massive image analysis. With high-speed microscopy, statistical evaluation of these measurements can be undertaken in a large population of cell nuclei which provides a way to estimate a probability of foci formation related to a particle traversal. These biological measurements are confronted with results obtained by Monte Carlo simulations, modeling the ionizing particle interactions on a virtual phantom of the cell nucleus with the same mean geometry and DNA density as the cells used. This should allow studying the relationship between the topology of energy deposition and early cell damaging. Knowing the different factors that drive the experimental uncertainties, we will be able to take them into account for the interpretation of the results. This allows us to obtain an accurate estimation of the probability of interaction, leading to foci formation, between particles of different LET and DNA.

DATA: 06-11-2014