Session Item

Due to their increased linear energy transfer, very heavy ions, like neon, provide a reduced oxygen enhancement effect. This could benefit the treatment of hypoxic tumours, which remains one of the major challenges in radiotherapy. However, clinical results in the 80’s led to adverse effects in healthy tissues and thus, the use of those beams was discontinued. One possible strategy to overcome this limitation is to combine the prominent advantages of these very heavy ions and the remarkable tissue preservation provided by the spatial fractionation of the dose, as in minibeam radiotherapy (MBRT). In this work, we will investigate the biochemical mechanisms involved in healthy tissue response after Ne MBRT (in vitro studies). For this purpose, we used the capabilities of synchrotron-based Fourier transform infrared microspectroscopy (SR-FTIRM) as a bio-analytical tool to elucidate the biological mechanisms induced by Ne MBRT at the molecular level and at a single-cell scale.

BJ human fibroblasts were irradiated using neon beams, in conventional and minibeam configurations, at the Heavy Ion Medical Accelerator in Chiba (HIMAC) of the National Institutes for Quantum Science and Technology (Japan). SR-FTIRM at ALBA Synchrotron (MIRAS beamline) was employed for examining composition and/or conformational changes in biomolecules, including proteins, lipids, carbohydrates, and nucleic acids. Principal Component Analysis (PCA) was performed using the Quasar software to evaluate the variations in the spectral features.

SR-FTIRM experiments allowed the characterization of spectral signatures of treatment-induced effects. PCA results showed clear differences between BB and MBRT groups with respect to Control, as it can be seen in Figure 1. The analysis of the PCA loadings plots reveals that most of the variance accounting for the separation between the peak and valley MBRT, the BB and the control groups is related to conformational changes in secondary protein structures, as well as to complex DNA conformational changes and rearrangements. Differences in the vibrational features were dose and time-dependent (data not shown).

Figure 1. SR-FTIRM results. Principal Component Analysis (PCA) (Left: PC1-PC2; Centre: PC2-PC3; Right: Loading plot) showing the differences between the several groups (Control: Ctrl; Broad beam: BB; Peak region in MBRT: MB_P; Valley region in MBRT: MB_V). Each point represents a cell spectrum.

Our study highlighted the relevance of SR-FTIRM as a useful and precise technique for assessing the biochemical cell response to innovative radiotherapy approaches. Results provided new insights into the molecular changes in response to MBRT treatments using neon beams. However, monitoring of overall cell response upon Ne MBRT is a complex task since it involves a wide range of biochemical processes.  The full understanding of the underlying biology in such novel approaches will require further investigations.