Highlights
- •Customized Timepix3 detector for characterization of stray radiation in UHDR beams.
- •The deposited energy, DR, and LET spectra were measured.
- •LET spectra exhibits the same characteristics regardless of the delivered DR.
- •At higher beam intensities a rescaling of LET can be performed.
- •A linear response of measured deposited energy was obtained at various DRs.
Abstract
Stray radiation produced by ultra-high dose-rates (UHDR) proton pencil beams is characterized
using ASIC-chip semiconductor pixel detectors. A proton pencil beam with an energy
of 220 MeV was utilized to deliver dose rates (DR) ranging from conventional radiotherapy
DRs up to 270 Gy/s. A MiniPIX Timepix3 detector equipped with a silicon sensor and
integrated readout electronics was used. The chip-sensor assembly and chipboard on
water-equivalent backing were detached and immersed in the water-phantom. The deposited
energy, particle flux, DR, and the linear energy transfer (LET(Si)) spectra were measured
in the silicon sensor at different positions both laterally, at different depths,
and behind the Bragg peak. At low-intensity beams, the detector is operated in the
event-by-event data-driven mode for high-resolution spectral tracking of individual
particles. This technique provides precise energy loss response and LET(Si) spectra
with radiation field composition resolving power. At higher beam intensities a rescaling
of LET(Si) can be performed as the distribution of the LET(Si) spectra exhibits the
same characteristics regardless of the delivered DR. The integrated deposited energy
and the absorbed dose can be thus measured in a wide range. A linear response of measured
absorbed dose was obtained by gradually increasing the delivered DR to reach UHDR
beams. Particle tracking of scattered radiation in data-driven mode could be performed
at DRs up to 0.27 Gy/s. In integrated mode, the saturation limits were not reached
at the measured out-of-field locations up to the delivered DR of over 270 Gy/s. A
good agreement was found between measured and simulated absorbed doses.
Keywords
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Article info
Publication history
Published online: January 17, 2023
Accepted:
January 3,
2023
Received in revised form:
December 22,
2022
Received:
April 30,
2022
Identification
Copyright
© 2023 Associazione Italiana di Fisica Medica e Sanitaria. Published by Elsevier Ltd. All rights reserved.
