Abstract
The response of Al2O3:C optically stimulated luminescence detectors (OSLDs) was investigated in a 250 MeV pencil proton beam. The OSLD response was mapped for a wide range of average dose rates up to 9000 Gy s−1, corresponding to a ∼150 kGy s−1 instantaneous dose rate in each pulse. Two setups for ultra-high dose rate (FLASH) experiments are presented, which enable OSLDs or biological samples to be irradiated in either water-filled vials or cylinders. The OSLDs were found to be dose rate independent for all dose rates, with an average deviation <1% relative to the nominal dose for average dose rates of (1–1000) Gy s−1 when irradiated in the two setups. A third setup for irradiations in a 9000 Gy s−1 pencil beam is presented, where OSLDs are distributed in a 3 × 4 grid. Calculations of the signal averaging of the beam over the OSLDs were in agreement with the measured response at 9000 Gy s−1. Furthermore, a new method was presented to extract the beam spot size of narrow pencil beams, which is in agreement within a standard deviation with results derived from radiochromic films. The Al2O3:C OSLDs were found applicable to support radiobiological experiments in proton beams at ultra-high dose rates.
Highlights
The use of radiotherapy with ultra-high dose rates (>40 Gy s−1, termed FLASH) has been studied for decades (Hornsey and Alper 1966, Town 1967) with renewed interest in recent years (Favaudon et al 2014, Vozenin et al 2019, Bourhis et al 2019a, 2019b)
Whilst the average of the front, center, and back optically stimulated luminescence detectors (OSLDs) doses would provide information about the dose delivered to biological samples placed in the water-filled cylinder, figure 7 shows the dose of the front OSLD nearest the nozzle as the dose varies through the cylinder
Al2O3:C Optically stimulated luminescence (OSL) were investigated in a pencil proton beam for a wide range of dose rates up to 9000 Gy s−1, which corresponds to an instantaneous dose rate about 150 kGy s−1 within each pulse
Summary
The use of radiotherapy with ultra-high dose rates (>40 Gy s−1, termed FLASH) has been studied for decades (Hornsey and Alper 1966, Town 1967) with renewed interest in recent years (Favaudon et al 2014, Vozenin et al 2019, Bourhis et al 2019a, 2019b). Few experiments have been conducted, if any, for dose rates >1000 Gy s−1 in clinically relevant proton beams due to accelerator limitations (Esplen et al 2020). For proton pencil beams with energies above 200 MeV, the highest dose rate is generally achieved in the entrance regions before the beam undergoes scattering. For dosimetry in such beams to support radiobiological experiments, one needs a detector capable of measuring a dose delivered with ultra-high dose rates, and that can be placed in a water-filled container depending on the type of biological sample
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