ESTRO 2025 - Abstract Book

S2629

Physics - Detectors, dose measurement and phantoms

ESTRO 2025

3370

Digital Poster 3D tomodosimetry with plastic scintillators for quality assurance in FLASH radiotherapy Eleonora Ravera 1,2 , Andrea Cavalieri 3,1 , Esther Ciarrocchi 1,2,3 , Fabio Di Martino 4,2 , Matteo Morrocchi 1,2,3 , Maria Giuseppina Bisogni 1,2,3 1 Physics, University of Pisa, Pisa, Italy. 2 Section of Pisa, National Institute of Nuclear Physics (INFN), Pisa, Italy. 3 Center for Instrument Sharing (CISUP), University of Pisa, Pisa, Italy. 4 U.O. Fisica Sanitaria (AOUP), Azienda Ospedaliero-Universitaria Pisana, Pisa, Italy Purpose/Objective: This contribution presents the development of a 3D online dosimeter based on a plastic scintillating monolithic block, imaged with cameras. The three-dimensional dose distribution delivered within the scintillator is reconstructed by applying a tomographic algorithm. We will discuss the performance of the detector and the algorithm, validated through simulations and beam tests using the electron FLASH LINAC accelerator at the Centro Pisano Flash Radiotherapy (CPFR) in Pisa. Material/Methods: The detector consists of a 10 cm polyvinyl-toluene-based plastic scintillator block (EJ200, Eljen Technology, Texas) positioned along the beamline to absorb a 9-MeV electron beam. Scintillation light emitted from the detector is captured by three cameras, each coupled to a focusing objective, and positioned along three orthogonal axes (Fig. 1) to collect the light emitted along directions parallel and orthogonal to the beam axis. A maximum likelihood approach is employed in the reconstruction algorithm to derive 3D dose maps from lateral light projections. Simulations and preliminary experimental tests have been performed, with a comprehensive characterization planned for the upcoming data-taking sessions.

Results: Fig. 2 presents our first simulation results showing the original simulated distributions (a, d), the reconstructed ones (b, e), and their respective differences (c, f), for two selected slices within the 3D volume. With respect to the reference system in Fig.1a, the top row is relative to a longitudinal slice, taken from the central xz plane, while the bottom row shows a transversale slice from the yz plane at x=1.2 cm (x=0 corresponds to the block entrance surface), where the build-up depth of the 9-MeV electron beam is expected. The simulated 3D dose distribution directly represents the dose delivered within the phantom, while the reconstructed distribution is derived by simulating the scintillation process and the light maps captured by the photodetectors, and then applying the tomographic reconstruction algorithm.