Presenter of 1 Presentation
OPTICALLY STIMULATED LUMINESCENCE DETECTORS (OSLDS) FOR ULTRA-HIGH DOSE RATE PROTON DOSIMETRY
Abstract
Background and Aims
The objective of this study was to assess the use of optically stimulated luminescence detectors (OSLDs) to support radiobiological experiments for ultra-high dose rates (FLASH) proton beams.
Methods
Two experimental setups were tested to accommodate either biological samples or multiple mm2-sized Al2O3:C OSLDs. The OSLDs were read out using a protocol with a reference irradiation under known conditions to account for material differences. The experiments were conducted in a single pencil beam at the PSI Gantry 1 at a wide dose rate range of (1-3800) Gy/s. A third experiment assessed the spot reconstruction at 9000 Gy/s.
Results
The OSLDs were demonstrated to be dose rate independent with a negligible signal fading. The OSLD evaluated doses were on average (n=66) within 1 % of the nominal dose for (3 – 33) Gy for dose-rates (1 – 1000) Gy/s. The discrepancy between the OSLDs and the nominal dose was higher for the (3800-9000) Gy/s dose rates due to averaging effects of the narrow pencil beam over the OSLD surface, where a correction was demonstrated. An OSLD dose measurement was overall found to be reproducible within 1 %. The use of an OSLD grid enabled an estimation of the beam spot size and position in agreement (deviation < 2%) with radiochromic film measurements.
Conclusions
The results demonstrate that the almost point-like OSLDs are applicable for accurate proton dosimetry in ultra-high dose rates and suitable to support radiobiological experiments in water and air.
Author Of 2 Presentations
OPTICALLY STIMULATED LUMINESCENCE DETECTORS (OSLDS) FOR ULTRA-HIGH DOSE RATE PROTON DOSIMETRY
Abstract
Background and Aims
The objective of this study was to assess the use of optically stimulated luminescence detectors (OSLDs) to support radiobiological experiments for ultra-high dose rates (FLASH) proton beams.
Methods
Two experimental setups were tested to accommodate either biological samples or multiple mm2-sized Al2O3:C OSLDs. The OSLDs were read out using a protocol with a reference irradiation under known conditions to account for material differences. The experiments were conducted in a single pencil beam at the PSI Gantry 1 at a wide dose rate range of (1-3800) Gy/s. A third experiment assessed the spot reconstruction at 9000 Gy/s.
Results
The OSLDs were demonstrated to be dose rate independent with a negligible signal fading. The OSLD evaluated doses were on average (n=66) within 1 % of the nominal dose for (3 – 33) Gy for dose-rates (1 – 1000) Gy/s. The discrepancy between the OSLDs and the nominal dose was higher for the (3800-9000) Gy/s dose rates due to averaging effects of the narrow pencil beam over the OSLD surface, where a correction was demonstrated. An OSLD dose measurement was overall found to be reproducible within 1 %. The use of an OSLD grid enabled an estimation of the beam spot size and position in agreement (deviation < 2%) with radiochromic film measurements.
Conclusions
The results demonstrate that the almost point-like OSLDs are applicable for accurate proton dosimetry in ultra-high dose rates and suitable to support radiobiological experiments in water and air.
GRAPHITE CALORIMETRY AND ALANINE FOR TRACEABLE DOSIMETRY IN PROTON FLASH BEAMS
Abstract
Background and Aims
A graphite calorimeter with a small core (5 mm diameter, 7 mm height) has been designed with the objective to characterize solid-state detectors in new radiotherapy modalities with respect to response changes resulting from changes in LET, dose rate and other parameters. Using a replica of the calorimeter, one can, for example, substitute the graphite core with the detector under investigation to obtain paired measurements with the graphite core and the detector under investigation under near-identical scatter conditions. In this study, we used the calorimeter to test alanine dosimetry for dose-rate effects in proton FLASH beams.
Methods
Measurements were performed at the Varian ProBeam system at the Danish Center of Particle beam using 250 MeV PBS beams with nozzle currents ranging from 4 nA to 215 nA (FLASH). For the main tests, we compared alanine pellets placed in the beam entrance with the temperature increase in the graphite core placed about 8 cm downstream.
Results
14 proton irradiations delivered doses of 10-11 Gy at different nozzle currents using a fixed 7 x 7 spot pattern (30 mm x 30.6 mm field size with a 50 Gy/s field dose rate for 215 nA nozzle current). The alanine doses correlated strongly with the temperature increases in the graphite core. Within experimental uncertainty, the ratio between alanine dose and temperature increase was found to be independent of the nozzle current in the tested dose rate range.
Conclusions
This study supports that alanine can be used for proton FLASH dosimetry without correction for dose-rate effects.