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TUAO03 |
Ionization Chamber for Electron Beam Monitoring at Ultra High Dose Rate | ||||
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Ultra high dose rate (FLASH) electron beam therapy consists in treating tumors by delivering a dose above 1 Gy in pulse of 1 µs. Despite ionization chambers are reference detectors in dose monitoring, no real-time beam monitor based on ionization chambers exists for such ultra high dose rates. In this study, we present the response of an ionization chamber to ultra high dose rates. Simulations were performed to compute the current measured by a chamber using a 1D transport model. The transport equations included recombination*, electron capture [**,***] and electric field change due to space charge****. Simulations were compared to measurements performed using a 800 µm gap, 1 cm2 active surface ionization chamber irradiated by 5 MeV electron pulses up to 4 Gy/µs, and varying high voltage from 400 V/mm up to 1200 V/mm. Despite high recombination rates, the signal produced by the electrons moving in the chamber was proportional to the dose rate up to ~100 ns. Preliminary results suggest that a real-time dose measurement can be done by considering only the signal induced by the electrons. This opens the development for a real-time dose rate monitor based on ionization chambers.
*J. W. Boag et al 1996 Phys. Med. Biol. 41 885 **F. Di Martino et al 2005 Med. Phys. Vol.32, No 7 ***K. Petersson et al 2017 Med. Phys. Vol.44, No 3 ****M. Gotz et al 2017 Phys. Med. Biol. 62 8634 |
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