3D dosimetry with plastic scintillators for quality assurance in FLASH radiotherapy

FLASH radiotherapy currently lacks an online three-dimensional dosimetric system capable of providing real-time information on the delivered dose distribution. This thesis investigates the feasibility of a scintillation-based volumetric dosimeter for electron FLASH radiotherapy based on a cubic EJ-200 plastic scintillator with a side length of 10 cm. The proposed approach is based on the acquisition of optical images of the scintillator from multiple lateral views during irradiation, which are then used to reconstruct the three-dimensional dose distribution through a tomographic reconstruction algorithm. The work includes the development of a Geant4 simulation framework, the adaptation and validation of a tomographic reconstruction algorithm, and the design and experimental characterization of a proof-of-concept detector using the 9 MeV electron FLASH beam available at the Centro Pisano FLASH Radiotherapy facility (Pisa). Particular attention was devoted to the study of optical artefacts, including internal reflections and refraction, and to the implementation of dedicated correction strategies integrated into the reconstruction framework.