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Monitoring Ultra-High Dose Rate (UHDR) beams is one of the multiple challenges posed by the emergent FLASH radiotherapy. Technologies (i.e., gas-filled ionization chambers) nowadays used in conventional radiotherapy are no longer effective when applied to UHDR regimes, due to the recombination effect they are affected by, and the time required to collect charges. Exploiting the expertise in the field of silicon sensors' applications into clinics, the medical physics group of the University and INFN Torino is investigating thin silicon sensors as possible candidates for UHDR beam monitoring, exploiting their excellent spatial resolution and well-developed technology. Silicon sensors of 30 and 45 μιτι active thicknesses and 0.25, 1 and 2 mm[sup 2] active areas were tested at the SIT ElectronFlash machine (CPFR, Pisa) on 9 MeV electron beams, featuring a pulse duration of 4 μ^ a frequency of 1 Hz, and a dose-per-pulse ranging from 1.62 to 10.22 Gy/pulse. The silicon sensors were positioned at the exit of the ElectronFlash applicator, after a solid water build-up slab, and were readout both with an oscilloscope and with a multi-channel front-end readout chip (TERA08). A response linearity extending beyond 10 Gy/pulse was demonstrated by comparison with a reference dosimeter (FlashDiamond), thus fulfilling the first requirement of a potential application in UHDR beam monitoring. [ABSTRACT FROM AUTHOR]

FLASH Radiotherapy (RT) delivers an average dose-rate >40 Gy/s in less than 200 ms with extremely high instantaneous dose-rates, and preclinical studies demonstrated a tumoricidal effect comparable to conventional RT with an increased sparing effect on healthy tissues (FLASH effect). Within the INFN-FRIDA project, we are exploring thin silicon sensors and polycrystalline CVD diamond (pCVD) sensors as real-time beam monitors for electron and proton FLASH beams. Planar silicon sensors were first tested on conventional electron beams and subsequently on high-dose electron beams (ElectronFLASH machine, funded by the Pisa Foundation). Diamond, due to some of its properties including radiation resistance, could also be a viable alternative for monitoring FLASH beams. The first tests were carried out in Turin, and the sensor response was studied in terms of polarization voltage, integrated charge, charge collection efficiency and sensitivity. [ABSTRACT FROM AUTHOR]