Orateur
Description
Cancer is a major public health issue, and radiotherapy is involved in the treatment in more of 50 % cases. It relies on the use of ionising radiation to damage, directly or indirectly the DNA of tumor cells. Conventional radiotherapy primarily uses photons and electrons, whose energy deposition extends along their path through the tissues. In contrast, ion beams allow for the concentration of dose deposition around the Bragg peak, thereby limiting the irradiation of healthy tissues. This property is the basis for the development of hadron therapy. However, the biological mechanisms associated with these irradiations, and in particular the relationship between linear energy transfer (LET) and cellular response, remain partially unknown. The BioALTO platform, currently under development at the ALTO accelerator (IJCLab), aims to study these mechanisms by allowing the irradiation of biological samples with various ions of interest for hadrontherapy.
In order to ensure the reliability and reproducibility of the irradiations, various diagnostics are arranged along the beam line. Notably, scintillating fibers detector from IP2I, a diamond detector from LPSC allowing the measurement of beam current, aluminas to visualize the beam, as well as a Faraday cage. However, some of these elements intercept the beam. In order to monitor the fluence and homogeneity of the beam as close as possible to the biological samples, a non-interceptive beam profiler is currently under development. It relies on the detection of air fluorescence: when the beam passes through air, nitrogen molecules are excited and emit photons in the near ultraviolet, with a peak emission around 337 nm. This light is detected by silicon photomultipliers (SiPM), which are compact and operate under low supply voltage. The device aims to monitor the intensity and position of the beam, as well as to characterise its spatial homogeneity and the associated dose.
A preliminary experimental study, conducted at the ARRONAX cyclotron, demonstrated the feasibility of the system, with a linear response of the signal as a function of the beam current. However, the measured noise currently limits the usable dynamic range of the detectors. The design of a chassis ensuring their electromagnetic shielding and the selection of the optimal SiPM is therefore underway.
In parallel, Monte Carlo simulations conducted with OpenGATE allow for the study of different geometries of optical fibers and collimators to optimise the collection of fluorescence photons and estimate the light flux reaching the SiPM. In the long term, image reconstruction algorithms, such as MLEM or OSEM, will be studied to reconstruct the spatial profile of the beam and quantify its inhomogeneity. This device thus aims to provide online control of irradiation conditions and to enhance the reliability of radiobiology experiments conducted on BioALTO.