• beam monitoring
• FLASH radiotherapy
• plastic scintillators

FLASH Radiotherapy (RT) is a new cancer radiotherapy technique where the therapeutic dose is delivered at dose rates of more than 40 Gy/s in less than 200 ms. Such ultra high dose rate (UHDR) irradiation triggers the so-called FLASH effect that, as observed in several animal models, is highly protective on normal tissues whilst still maintaining the efficacy on tumors. As of now, clinical trials have to be conducted to verify if these results can be replicated in human patients. Hence, beam monitoring systems and active dosimeters are fundamental to perform reliable preclinical experiments and to safely deploy human clinical trials. At such high DPP values, conventional active dosimeters like ion chambers show significant recombination. Recently, scintillator based detectors have been explored as dosimeters for UHDR beams, including 2D dosimetry and beam monitoring.
The aim of this work is to develop an imaging system based on a scintillating sheet for UHDR beam monitoring. The scintillating sheet is coupled with a Charged-Coupled Device camera (CCD) and produces 2D images in real time of the irradiation field produced by a 9 MeV UHDR electron beam impinging on it. The first step was to develop a Monte Carlo simulation of the experimental set-up using the Geant4 toolkit. In particular, the geometry reproduces the SIT-ElectronFLASH LINAC of the Centro Pisano per la Flash Radiotherapy (CPFR) installed at the Santa Chiara University Hospital where also the measurements were carried out. The purpose of the measurements was to demonstrate the linearity of the response of the system with the DPP. To investigate the dependency of the response from the beam energy, Percentage Depth Dose (PDD) measurements have been also performed in a plastic phantom and compared with the simulations and with a reference dosimeter.