Dottorato in FISICA DEGLI ACCELERATORI

Titolo della tesi: Development of a fluorescence-based beam monitor and beam delivery studies for FLASH radiotherapy

In the contemporary world of cancer treatment, conventional radiotherapy has been instrumental in targeting tumorous pathologies. However, this method is not without limitations, especially in cases involving radioresistant tumors and delicate, vital organs. To address these challenges, efforts have been made to improve the precision and effectiveness of radiotherapy. One promising development is the FLASH effect, where ultra-high dose rates of radiation (~100$ Gy/s) are delivered in an exceptionally short time (<500 ms), resulting in reduced damage to healthy tissues. This thesis explores two of the main topical issues in today's efforts for the implementation of the FLASH effect in clinical practice. The first challenge lies in beam monitoring at ultra-high dose rates. Conventional radiotherapy relies on detectors to monitor the therapeutic beam, but standard devices often saturate and degrade their performances at FLASH intensities. This thesis explores an innovative approach using air fluorescence as a beam monitoring technique. I developed three detector prototypes to evaluate this technique, demonstrating its feasibility, and obtained promising results in terms of temporal resolution and linearity with beam current, while also highlighting the need for further refinement in the readout system to improve signal-to-noise ratio. The second challenge is delivering the ultra-high dose rapidly while maintaining precision in spatial conformity of the dose to the tumour volume. Traditional methods involving multiple field configurations and varying energies need to be carefully adapted to meet the requirements for FLASH therapy, particularly for deep-seated tumors. The thesis discusses a solution based on a high-energy electron accelerator project known as the SAFEST project, which aims to develop a compact beam delivery system for FLASH radiotherapy. The proposed system employs active particle scanning using a system of magnetic dipoles coupled with a static toroidal gantry. Analytical calculations and simulations are used to assess the feasibility of this approach, with plans for further optimization and testing. Keywords: FLASH effect, beam monitoring, fluorescence, active scanning.