Performance of SiC Diodes at Very High Doses of Low-Energy Proton Beams Under FLASH Conditions

FLASH therapy has emerged as a promising radiotherapy technique, minimizing damage to healthy tissues while maintaining effective tumor control. Achieving FLASH conditions requires dose rates exceeding 40 Gy/s, but conventional dosimetry systems fail under these conditions. Recently, IMB-CNM (CSIC) developed SiC p-n diodes with 30 μm diameter and 3 μm thickness, specifically designed for FLASH radiotherapy. This study investigates their response to low-energy UHDR proton beams after high and ultra-high accumulated doses for the first time. Experiments were performed in the 3 MV tandem accelerator at CNA using 1 MeV and 2 MeV protons with a pulsed beam system, achieving mean dose rates of 10 kGy/s, dose-per-pulse of 5.6 Gy, and dose rate within the pulse of 4.6 MGy/s. Ion pulses were characterized using a Faraday Cup and Rutherford Backscattering Spectrometry (RBS). Two SiC diodes were studied: one pre-irradiated with 3.6 MGy for extreme applications and another for early irradiation stages. The pre-irradiated diode showed a sensitivity decrease of -1.34 %/kGy up to 750 kGy, stabilizing within 7 % response variation up to 4.5 MGy. The response remained linear within 10 % at mean dose rate up to 5 kGy/s for 2 MeV protons, demonstrating the feasibility of this technology for FLASH applications.