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Particle and radiation therapy are leading tactics to combat chronic and malignant cancers. Ultra-high dose rate proton therapy promises higher radiobiological advantage and increased effectiveness in targeting tumor cells while sparing healthy cells, by providing the total dose in a short time at a rate higher than 40 Gy/s .
This work aims to characterize the charge acquisition of hydrogenated amorphous silicon (a-Si) pixels under proton flash irradiation. A-Si gains particular interest due to its capacity to produce large-scale and high-resolution flat panel detectors at an affordable cost with improved radiation hardness.
A test board of 2.4 x 2.4 mm aSi pixel array was acquired and bonded to test under flash proton irradiation at MedAustron in Vienna. The test plan was to irradiate using a single spot at different spill lengths and spill numbers to test the behavior from conventional to flash regimes for dose rate dependence measurements. Additionally, a calibrated ionization chamber fitted for flash proton measurements (IBA PPC05) was placed at the isocenter for dose and spill length verification. The chamber was connected to the IBA DoseX electrometer equipped with an API measuring at a rate of 1 KHz. A Flat Panel was placed behind the pixels for beam spot positioning.
Analyzing dose rate dependence, measurements were normalized twice by the dose measured via the PPC05 and the average. The integration time was kept the same at 10s for all measurements. At higher dose rates, the normalized charge increases until it reaches a plateau, then saturates in the flash regime. This is expected since at higher current, charge traps get filled the higher the dose rate, until all the charge traps saturate.
To test for radiation hardness, dose sensitivity was measured before and after heavy irradiation of 5.56 × 1010 protons (in the active region) using a clinical map. The sensitivity was reduced by 10%.
The results show proper reproducibility and dose linearity. With calibration needed for dose rate dependence. Additional irradiation campaigns are planned soon to examine the Bragg peak quenching at different bias voltages.