###### Abstract  
Fourier transform infrared microspectroscopy using a synchrotron radiation source (SR-\(\upmu\)FTIR) has great potential in the study of the ionizing radiation effects of human cells by analyzing the biochemical changes occurring in cell components. SR-\(\upmu\)FTIR spectroscopy has been usefully employed in recent years in some seminal work devoted to shedding light on processes occurring in cells treated by hadron therapy, that is, radiotherapy with charged heavy particles (mainly protons and carbon ions), which is gaining popularity as a cancer treatment modality. These studies are particularly useful for increasing the effectiveness of radiotherapy cancer treatments with charged particles that can offer significant progress in the treatment of deep-seated and/or radioresistant tumors. In this paper, we present a concise revision of these studies together with the basic principles of \(\upmu\)FTIR spectroscopy and a brief presentation of the main characteristics of infrared SR sources. From the analysis of the literature regarding the SR-\(\upmu\)FTIR spectroscopy investigation on human cells exposed to proton beams, it is clearly shown that changes in DNA, protein, and lipid cell components are evident. In addition, this review points out that the potential offered by SR-\(\upmu\)FTIR in investigating the effects induced by charged particle irradiation have not been completely explored. This is a crucial point for the continued improvement of hadron therapy strategies.  
Fourier transform infrared microspectroscopy; infrared synchrotron radiation; human cells; proton irradiation; hadron therapy +
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\(\mu\)FTIR spectroscopy has also been demonstrated to be a useful tool in radiobiology, since it can rapidly and non-invasively investigate the complex biological processes occurring in cells exposed to ionizing radiation, such as proliferation and cell death processes, and it has attracted a growing interest in the field of radiation-induced cyto- and genotoxicity [13; 14; 15; 16; 17; 18; 19]. In addition, in this field, \(\mu\)FTIR spectroscopy has benefited from the use of SR sources managing to study single cells in an aqueous environment [16; 20; 21; 22; 23].  
Over the last years, hadron therapy that uses charged particles, as protons and carbon ions, has acquired a noticeable importance in radiotherapy treatment due to the several advantages that charged particles give in comparison to photons [24; 25]. Charged particles release most of their energy at the end of their range; thus, they offer a much better localization of the dose distribution within the tumor volume in comparison to X-rays. In this way, the transfer of very high-dose gradients close to organs at risk is allowed, and the high-dose area is confined to the tumor volume. However, significant improvement in hadron therapy outcomes is strictly related to the possibility of obtaining fast and accurate information on cell response. For this purpose, some researchers recognized the potential of SR sources and \(\mu\)FTIR spectroscopy for enlightening the complex processes occurring after cell exposure to proton beams.  
In this paper, we aimed at presenting a concise review of these studies together with the basic principles of \(\mu\)FTIR spectroscopy and a brief presentation of the principal characteristics of infrared radiation synchrotron sources.