Ionization quenching in scintillators used for dosimetry of mixed particle fields

Christensen, Jeppe Brage; Almhagen, Erik; Stolarczyk, Liliana; Vestergaard, A.; Bassler, Niels; Andersen, C.E.

doi:10.1088/1361-6560/ab12f2

Cited by 13 publications

(12 citation statements)

References 28 publications

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“…Such an analysis had not been done for BaFBr 0.85 I 0.15 :Eu 2+ dosimeters but it is also likely that they will lead to similar findings given the related PSL mechanisms of the two inorganic dosimeters. However, we have since noted a successful application of a more fundamental and quantitative alternative to the cylindrical infratrack theory by Christensen et al to organic plastic scintillators 48 and for our future work, we will be investigating the theoretically predicted quenching magnitudes of BaFBr 0.85 I 0.15 :Eu 2+ dosimeters using this more fundamental approach.…”

Section: Discussionmentioning

confidence: 99%

“…41 Their applicability in describing physical effects such as the experimental under-responses is a choice that seems to be detector dependent. For instance, Christensen et al, had shown that track-averaged LET values were more accurate in predicting the magnitude of proton quenching of plastic scintillators 48 whereas other authors have shown that dose-averaging was a more accurate measure for other dosimeters such as OSLDs 25 and radiochromic films. 26,49 As such, it is important for us to determine the more accurate averaging scheme (dose-or track-averaging) that is more relevant to BaFBr 0.85 I 0.15 :Eu 2+ dosimeters.…”

Section: G Analytical Proton Stopping Power Ratio and Experimentalmentioning

confidence: 99%

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Dual‐storage phosphor proton therapy dosimetry: Simultaneous quantification of dose and linear energy transfer

et al. 2021

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To investigate the feasibility of using the high Z eff storage phosphor material BaFBrI:Eu 2+ in conjunction with the low Z eff storage phosphor material KCl:Eu 2+ for simultaneous proton dose and linear energy transfer (LET) measurements by (a) measuring the fundamental optical and dosimetric properties of BaFBrI:Eu 2+ , (b) evaluating its compatibility in being readout simultaneously with KCl:Eu 2+ dosimeters, and (c) modeling and validating its LET dependence under elevated proton LET irradiation. Methods: A commercial BaFBrI:Eu 2+ storage phosphor detector (Model ST-VI, Fujifilm) was characterized with energy dispersive x-ray spectroscopy (EDS) analysis to obtain its elemental composition. The dosimeters were irradiated using both a Mevion S250 proton therapy unit (at the center of a spread-out Bragg peak, SOBP) and a Varian Clinac iX linear accelerator with the latter being a low LET irradiation. The photostimulated luminescence (PSL) emission spectra, excitation spectra, and luminescent lifetimes of the detector were measured after proton and photon irradiations. Dosimetric properties including dose linearity, dose rate dependence, radiation hardness, temporal, and readout stabilities were studied using a laboratory optical reader after proton irradiations. In addition, its proton energy dependence was analytically modeled and experimentally validated by irradiating the detectors at various depths within the SOBP (Range: 15.0 g/ cm 2 , Modulation: 10.0 g/cm 2 ). Results: The active detector composition for the high Z eff storage phosphor detector was found to be BaFBr 0.85 I 0.15 :Eu 2+ . The BaFBr 0.85 I 0.15 :Eu 2+ material's excitation and emission spectra were in agreement under proton and photon irradiations, with peaks of 586 AE 1 nm and 400 AE 1 nm, respectively, with a full width at half maximum (FWHM) of 119 AE 3 nm and 30 AE 2 nm, respectively. As dosimeter response under photon irradiation is generally believed to be free from LET effect, these results suggest LET independence of charge storage center types resulted from ionizing radiations. There is sufficient spectral overlaps with KCl:Eu 2+ dosimeters allowing both dosimeters to be readout under equivalent readout conditions, that is, 594 nm stimulation and 420 nm detection wavelengths. Its PSL characteristic lifetime was found to be less than 5 microseconds which would make it suitable for fast 2D readout post irradiation. Its 420 nm emission band intensity was found to be linear up to 10 Gy absolute proton dose under the same irradiation conditions, dose rate independent, stable in time and under multiple readouts, and with high radiation hardness under cumulative proton dose histories up to 200 Gy as tested in this study. BaFBr 0.85 I 0.15 :Eu 2+ showed significant proton energy-dependent dose under-response in regions of high LET which could be modeled by stopping power ratio calculations with an accuracy of 3% in low LET regions and a distance-toagreement (DTA) of 1 mm in high LET regions (>5 keV/μm). Conclusion:We have proven the feasibi...

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Section: Discussionmentioning

confidence: 99%

Section: G Analytical Proton Stopping Power Ratio and Experimentalmentioning

confidence: 99%

Dual‐storage phosphor proton therapy dosimetry: Simultaneous quantification of dose and linear energy transfer

et al. 2021

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“…The OSLDs are omitted from the simulations for two reasons. Firstly, since a study 9 showed that the signal averaging over 1 mm wide plastic detectors was in proton beams, the signal averaging over the powder layer is expected to be negligible. Secondly, the OSLDs are calibrated in terms of dose and LET in water.…”

Section: Methodsmentioning

confidence: 99%

“…Ionization quenching is occasionally exploited to estimate the LET by comparing the response of two detectors having different quenching characteristics, e.g. scintillators relative to absorbed dose calorimeters 8 or scintillators relative to ionization chambers 9 . Similarly, pairs of differently quenching organic scintillators 10 , thermoluminescent detectors 11 or phosphor films 12 have been used to simultaneously estimate dose and LET, which, however, is associated with large uncertainties in regions with steep gradients, e.g.…”

Section: Introductionmentioning

confidence: 99%

Improved simultaneous LET and dose measurements in proton therapy

Christensen

Togno

Bossin

et al. 2022

Sci Rep

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The objective of this study was to improve the precision of linear energy transfer (LET) measurements using $$\text {Al}_2\text {O}_3\text {:C}$$ Al 2 O 3 :C optically stimulated luminescence detectors (OSLDs) in proton beams, and, with that, improve OSL dosimetry by correcting the readout for the LET-dependent ionization quenching. The OSLDs were irradiated in spot-scanning proton beams at different doses for fluence-averaged LET values in the (0.4–6.5) $$\hbox {keV}\, \upmu \hbox {m}^{-1}$$ keV μ m - 1 range (in water). A commercial automated OSL reader with a built-in beta source was used for the readouts, which enabled a reference irradiation and readout of each OSLD to establish individual corrections. Pulsed OSL was used to separately measure the blue (F-center) and UV ($$F^+$$ F + -center) emission bands of $$\text {Al}_2\text {O}_3\text {:C}$$ Al 2 O 3 :C and the ratio between them (UV/blue signal) was used for the LET measurements. The average deviation between the simulated and measured LET values along the central beam axis amounts to 5.5% if both the dose and LET are varied, but the average deviation is reduced to 3.5% if the OSLDs are irradiated with the same doses. With the measurement procedure and automated equipment used here, the variation in the signals used for LET estimates and quenching-corrections is reduced from 0.9 to 0.6%. The quenching-corrected OSLD doses are in agreement with ionization chamber measurements within the uncertainties. The automated OSLD corrections are demonstrated to improve the LET estimates and the ionization quenching-corrections in proton dosimetry for a clinically relevant energy range up to 230 MeV. It is also for the first time demonstrated how the LET can be estimated for different doses.

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“…(1) . Following Christensen et al [30] , the LET d values included in the model were scored from the entrance to the 80% distal dose point.…”

Section: Methodsmentioning

confidence: 99%

Empirical quenching correction in radiochromic silicone-based three-dimensional dosimetry of spot-scanning proton therapy

Valdetaro

Høye

Skyt

et al. 2021

Physics and Imaging in Radiation Oncology

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Background and purpose: Three-dimensional dosimetry of proton therapy (PT) with chemical dosimeters is challenged by signal quenching, which is a lower dose-response in regions with high ionization density due to high linear-energy-transfer (LET) and dose-rate. This study aimed to assess the viability of an empirical correction model for 3D radiochromic silicone-based dosimeters irradiated with spot-scanning PT, by parametrizing its LET and dose-rate dependency. Materials and methods: Ten cylindrical radiochromic dosimeters (Ø50 and Ø75 mm) were produced in-house, and irradiated with different spot-scanning proton beam configurations and machine-set dose rates ranging from 56 to 145 Gy/min. Beams with incident energies of 75, 95 and 120 MeV, a spread-out Bragg peak and a plan optimized to an irregular target volume were included. Five of the dosimeters, irradiated with 120 MeV beams, were used to estimate the quenching correction factors. Monte Carlo simulations were used to obtain dose and dose-averaged-LET (LET d ) maps. Additionally, a local dose-rate map was estimated, using the simulated dose maps and the machine-set dose-rate information retrieved from the irradiation log-files. Finally, the correction factor was estimated as a function of LET d and local dose-rate and tested on the different fields. Results: Gamma-pass-rates of the corrected measurements were >94% using a 3%-3 mm gamma analysis and >88% using 2%-2 mm, with a dose deviation of <5.6 ± 1.8%. Larger dosimeters showed a 20% systematic increase in dose-response, but the same quenching in signal when compared to the smaller dosimeters. Conclusion:The quenching correction model was valid for different dosimeter sizes to obtain relative dosimetric maps of complex dose distributions in PT.

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Ionization quenching in scintillators used for dosimetry of mixed particle fields

Cited by 13 publications

References 28 publications

Dual‐storage phosphor proton therapy dosimetry: Simultaneous quantification of dose and linear energy transfer

Dual‐storage phosphor proton therapy dosimetry: Simultaneous quantification of dose and linear energy transfer

Improved simultaneous LET and dose measurements in proton therapy

Empirical quenching correction in radiochromic silicone-based three-dimensional dosimetry of spot-scanning proton therapy

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