ESTRO 2024 - Abstract Book

S4676

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTR0 2024

In order to accurately reproduce biological responses occurring when living cells are exposed to ionizing radiation, it is necessary to properly reproduce the physical interactions of this radiation with matter, as well as its chemical effects, such as the radiolysis of the different molecules composing the cells (water, proteins, DNA…). While several studies have addressed the question of physical properties of secondary particles produced by high energy ions, the crucial chemical aspect, that makes the link between physical and biological effects of radiations, is often neglected. The CLINM (Cross-Sections of Light Ions and Neutron Measurements) project, funded by ANR (starting in January 2024), seeks to offer a global characterization of the secondary particles produced by fragmentation processes of ions on tissues, and their associated chemical effects.

Material/Methods:

The investigation of these chemical effects involves the measurement of the radiolysis products generated by the secondary particles, while the physical properties (energy, charge) of these particles is performed thanks to a DE-E telescope. A first experimental campaign of the CLINM project was performed at the CNAO hadrontherapy center (Pavia, Italy), and the achieved results of this campaign will be presented in this work. In this experiment, a 12C ion beam with various energies (200, 300 and 400 MeV/u) was degraded by different thicknesses of target (5, 15 and 23 cm of RW3), in order to achieve an identical energy of 120 MeV/u after the target. Samples were placed after the target in order to study the water radiolysis generated by the beam and its resulting secondary particles. In order to characterize the particles field, and therefore enhance the accuracy of the dose in the samples, the DE-E telescope was used in the same conditions. This telescope is made of a thin plastic scintillator (2 mm) placed in front of a cerium bromide crystal scintillator (CeBr3). It was placed behind the RW3 target (tissue equivalent material), and sets at two different angles (0 and 5º). A calibration process was conducted at various facilities, allowing to evaluate the response of the detectors over a wide range of energies (between 1 MeV up to several GeV).

Results:

The results obtained from this experiment demonstrate the importance of the experimental characterization of secondary particles fields. For instance, looking into the experimental and simulated energy distributions of Z=2 ions produced by 400MeV/u 12C ions on RW3 target (at 0º), important differences are observed between simulation (carried out with Geant4) and data. In that specific case, a factor 2 in the measured energy is observed between the simulation and the experiment. Furthermore, while the energy simulations for other Z-values appear more consistent, important discrepancies emerge in the production yield of particles, as depicted in Figure 1.