ESTRO 2025 - Abstract Book

S2671

Physics - Detectors, dose measurement and phantoms

ESTRO 2025

This work investigates the potential of a hydrogenated amorphous silicon (a-Si:H) PIN sensor matrix, deposited on a flexible Kapton substrate, for studying the temporal structure of high-dose rate electron (HDRE) beams. These exploratory measurements aim to pave the way for potential dosimetric applications in FLASH radiotherapy. Material/Methods: The sensor features a 5×6 matrix of pixels, each measuring 2×2 mm², with a 0.4 μm intrinsic layer of hydrogenated amorphous silicon. The contacts are made using chromium and aluminium, and the entire matrix is deposited on a 60 μm Kapton substrate, ensuring flexibility. Signals are read using a TetrAMM picoammeter with one bias channel and four high-speed current readout channels operating at 100 kHz. All measurements were conducted without external bias voltage, simplifying the setup and enhancing reliability. Clinical 8MeV electron beams at the Radiotherapy Unit of the Azienda Ospedaliero Universitaria Careggi , were used to irradiate at the maximum depth, SSD=98,4cm e 10x10cm 2 field size in order to evaluate its ability to resolve the beam’s temporal structure. Measurements focused on reconstructing individual electron bunches and analysing variations in their repetition rates across a range of dose rates. Results: Fig.1a shows single beam bunches as obtained from the sensor read out with the Tetramm picoammeter. This simple setup has already a time resolution fully sufficient to resolve single beam pulses at all the typical clinical pulse repetition frequencies. This is particularly important in view of a possible use of such sensors in non-standard regimes such as those used in FLASH therapy. A zoom of single pulses is shown in fig.1b. The lower amplitude pulses are those obtained in standard linac configuration while the high amplitude signals correspond to HDRE setup. As it can be seen from tab.1, the measured current in the two setups show a fairly good linearity, providing a first indication of the large dynamical range of these dosimeters.