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

Setianegara, Jufri; Mazur, Thomas R.; Yang, Deshan; Li, H. Harold

doi:10.1002/mp.14748

Cited by 7 publications

(11 citation statements)

References 74 publications

(142 reference statements)

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“…The CCD of the Lynx scintillation detector measures discrete pixel counts ranging from 1 to 1000 and this will impose a maximum theoretical dynamic range of 1000:1. While this dynamic range is already respectable and useful for versatile dosimetry purposes, storage phosphors can confer an even higher dynamic range as they are able to measure absorbed doses‐to‐water that are as low as 0.01 cGy and high doses of up to 60 Gy without any saturation effects 18‐20,29,30 . Having a dosimeter with a wide dynamic range is important for the expedient measurement of proton halo effects as their doses are typically on the order of 0.1% of the peak proton dose 13 .…”

Section: Discussionmentioning

confidence: 99%

“…Square 5 × 5 cm 2 dosimeter samples were cut from a BaFBrI:Eu 2+ ‐based storage phosphor dosimeter panel (Model ST‐VI, Fujifilm). Its exact elemental composition was previously characterized to be BaFBr 0.85 I 0.15 :Eu 2+ with energy dispersive X‐ray spectroscopy (EDS) analysis using scanning electron microscopy (Thermofisher Quatro Environmental SEM) 19 . These samples were then affixed onto a 7 by 5 cm acrylic base cutout (Figure 1b) with ±1 cm extensions beyond the panel in the x ‐axis.…”

Section: Methodsmentioning

confidence: 99%

“…Thus, inspired by our recent successes in the use of reusable storage phosphors for proton dose and linear energy transfer (LET) measurements of a proton beam, 18,19 we have developed an independent dosimetric system consisting of an in‐house optical scanner and reusable BaFBrI:Eu 2+ storage phosphors as a viable independent solution for accurate sub‐millimeter two‐dimensional (2D) proton dosimetric measurements. As compared with the commercial scintillation detector, BaFBrI:Eu 2+ storage phosphors have the added advantage of attaining a wider dynamic range under proton irradiation, 19 and its less bulky thin film geometry allows for an easier setup. In addition, storage phosphor films can attain a sub‐millimeter spatial resolution easily 20 and if the scanner settings are properly optimized, may even attain a slightly better spatial resolution than the commercial detector.…”

Section: Introductionmentioning

confidence: 99%

“…The latent charges remaining after readout can be erased completely 21 with a bright, broadband light which will render the material reusable. Previously, we demonstrated that these materials are radiation resistant up to proton dose tolerances of 200 Gy without any evidence of dose history effects, 19 thus allowing for multiple reuses without recalibration.…”

Section: Introductionmentioning

confidence: 99%

“…Thus, inspired by our recent successes in the use of reusable storage phosphors for proton dose and linear energy transfer (LET) measurements of a proton beam, 18,19 we have developed an independent dosimetric system consisting of an in-house optical scanner and reusable BaFBrI:Eu 2+ storage phosphors as a viable independent solution for accurate sub-millimeter twodimensional (2D) proton dosimetric measurements. As compared with the commercial scintillation detector, BaFBrI:Eu 2+ storage phosphors have the added advantage of attaining a wider dynamic range under proton irradiation, 19 and its less bulky thin film geometry allows for an easier setup. In addition, storage phosphor films (c) 24 dB/oct low pass filter slope, and (d) 160 Hz chopping frequency resulted in the highest SNR while maintaining sub-millimeter spatial resolution.…”

Section: Introductionmentioning

confidence: 99%

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Development of a storage phosphor imaging system for proton pencil beam spot profile determination

et al. 2021

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Purpose Accurate two‐dimensional (2D) profile measurements at submillimeter precision are necessary for proton beam commissioning and periodic quality assurance (QA) purposes and are currently performed at our institution with a commercial scintillation detector (Lynx PT) with limited means for independent checks. The purpose of this work was to create an independent dosimetry system consisting of an in‐house optical scanner and a BaFBrI:Eu2+ storage phosphor dosimeter by: (a) determining the optimal settings for the optical scanner, (b) measuring 2D proton spot profiles with the storage phosphors, and (c) comparing them to similar measurements using a commercial scintillation detector. Methods An in‐house 2D laboratory optical scanner was constructed and spatially calibrated for accurate 2D photostimulated luminescence (PSL) dosimetry. Square 5 × 5 cm2 BaFBrI:Eu2+ dosimeter samples were uniformly irradiated with line scans performed to determine the physical and electronic scanner settings resulting in the highest signal‐to‐noise ratios (SNR) at a sub‐millimeter spatial resolution. The resultant spatial resolution of the scanner was then quantitatively assessed by measuring (a) line pairs on a standard X‐ray lead bar phantom and (b) modulation transfer functions. Following this, 2D proton spot profiles from a Mevion S250i Hyperscan proton unit were obtained at 1, 10, 20, 30, 40, and 50 monitor unit (MU) settings at maximum energy (E0 = 227.1 MeV) and compared to baseline profiles from a commercial scintillation detector, where 1 MU is calibrated to deliver 1 Gy absolute proton dose‐to‐water under reference conditions, that is, 41 × 41 proton spots uniformly spaced by 0.25 cm within a 10 × 10 cm2 square field size at maximum energy (227.1 MeV) in water at depth of 5 cm at isocenter. The dosimetric system's sensitivities to (a) ±1 mm positional shifts and (b) ±0.3 mm beam lateral spread changes were quantitatively evaluated through a Gaussian fitting of the crossline and inline plots of the respective artificially shifted beam profiles. Results The physical scanner settings of (a) Δτ = 27 ms time interval between data samples, (b) vx = 1.235 cm/s scanning speed, (c) 1% laser transmission (0.02 mW power) and (d) (Δx, Δy) = (0.33, 0.50 mm) pixel sizes with electronic settings of (a) 300 microseconds time constant, (b) normal dynamic reserve, (c) 24 dB/oct low pass filter slope, and (d) 160 Hz chopping frequency resulted in the highest SNR while maintaining sub‐millimeter spatial resolution. The BaFBr0.85I0.15:Eu2+ storage phosphor dosimeters were linear from 1 to 50 MU and their profiles did not saturate up to 150 MU. The scanner was able to detect lateral displacements of ±1 mm in both the crossline and inline directions and ±0.3 mm beam spread changes that were artificially introduced by varying the incident proton energy. Specific to our proton unit, proton energy changes of ±1 MeV can also be detected indirectly via beam spread measurements. Conclusion Our combined dosimetric system including an in‐hous...

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…Thus, inspired by our recent successes in the use of reusable storage phosphors for proton dose and linear energy transfer (LET) measurements of a proton beam, 18,19 we have developed an independent dosimetric system consisting of an in-house optical scanner and reusable BaFBrI:Eu 2+ storage phosphors as a viable independent solution for accurate sub-millimeter twodimensional (2D) proton dosimetric measurements. As compared with the commercial scintillation detector, BaFBrI:Eu 2+ storage phosphors have the added advantage of attaining a wider dynamic range under proton irradiation, 19 and its less bulky thin film geometry allows for an easier setup. In addition, storage phosphor films (c) 24 dB/oct low pass filter slope, and (d) 160 Hz chopping frequency resulted in the highest SNR while maintaining sub-millimeter spatial resolution.…”

Section: Introductionmentioning

confidence: 99%

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Development of a storage phosphor imaging system for proton pencil beam spot profile determination

et al. 2021

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Calibration and time fading characterization of a new optically stimulated luminescence film dosimeter

Marco

Delombaerde²,

Marijke

et al. 2022

Medical Physics

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Background: Optically stimulated luminescence (OSL) dosimeters produce a signal linear to the dose, which fades with time due to the spontaneous recombination of energetically unstable electron/hole traps. When used for radiotherapy (RT) applications, fading affects the signal-to-dose conversion and causes an error in the final dose measurement. Moreover, the signal fading depends to some extent on treatment-specific irradiation conditions such as irradiation times. Purpose: In this work, a dose calibration function for a novel OSL film dosimeter was derived accounting for signal fading. The proposed calibration allows to perform dosimetry evaluation for different RT treatment regimes. Methods: A novel BaFBr:Eu 2+ -based OSL film (Z eff, 6 MV = 4.7) was irradiated on a TrueBeam STx using a 6 MV beam with setup: 0 • gantry angle, 90 cm SSD, 10 cm depth, 10 × 10 cm 2 field. A total of 86 measurements were acquired for dose-rates ( Ḋ) of 600, 300, and 200 MU/min for irradiation times (t ir ) of 0.2, 1, 2, 4.5, 12, and 23 min and various readout times (t scan ) between 4 and 1440 min from the start of the exposure (beam-on time). The OSL signal, S( Ḋ, t ir , t scan ), was modeled via robust nonlinear regression,and two different power-law fading models were tested, respectively, independent (linear model) and dependent on the specific t ir (delivery-dependent model). Results: After 1 day from the exposure, the error on the dose measurement can be as high as 48% if a fading correction is not considered. The fading contribution was characterized by two accurate models with adjusted-R 2 of 0.99. The difference between the two models is <4.75% for all t ir and t scan . For different beam-on times, 3, 10.5, and 20 min, the optimum t scan was calculated in order to achieve a signal-to-dose conversion with a model-related error <1%.In the case of a 3 min irradiation, this condition is already met when the OSLfilm is scanned immediately after the end of the irradiation. For an irradiation of 10.5 and 20 min, the minimum scanning time to achieve this model-related error increases, respectively, to 30 and 90 min. Under these conditions, the linear model can be used for the signal-to-dose conversion as an approximation of the delivery-dependent model.The signal-to-dose function,D(M i,j ,t scan ),has a residual mean error of 0.016, which gives a residual dose uncertainty of 0.5 mGy in the region of steep signal fading (i.e.,t scan = 4 min).The function of two variables is representable as a dose surface depending on the signal (M i,j ) measured for each i,j-pixel and the time of scan (t scan ). Conclusions: The calibration of a novel OSL-film usable for dosimetry in different RT treatments was corrected for its signal fading with two different models. A

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Characterizing devices for validation of dose, dose rate, and LET in ultra high dose rate proton irradiations

Harrison,

Charyyev,

Oancea

et al. 2024

Medical Physics

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BackgroundUltra high dose rate (UHDR) radiotherapy using ridge filter is a new treatment modality known as conformal FLASH that, when optimized for dose, dose rate (DR), and linear energy transfer (LET), has the potential to reduce damage to healthy tissue without sacrificing tumor killing efficacy via the FLASH effect.PurposeClinical implementation of conformal FLASH proton therapy has been limited by quality assurance (QA) challenges, which include direct measurement of UHDR and LET. Voxel DR distributions and LET spectra at planning target margins are paramount to the DR/LET‐related sparing of organs at risk. We hereby present a methodology to achieve experimental validation of these parameters.MethodsDose, DR, and LET were measured for a conformal FLASH treatment plan involving a 250‐MeV proton beam and a 3D‐printed ridge filter designed to uniformly irradiate a spherical target. We measured dose and DR simultaneously using a 4D multi‐layer strip ionization chamber (MLSIC) under UHDR conditions. Additionally, we developed an “under‐sample and recover (USRe)” technique for a high‐resolution pixelated semiconductor detector, Timepix3, to avoid event pile‐up and to correct measured LET at high‐proton‐flux locations without undesirable beam modifications. Confirmation of these measurements was done using a MatriXX PT detector and by Monte Carlo (MC) simulations.ResultsMC conformal FLASH computed doses had gamma passing rates of >95% (3 mm/3% criteria) when compared to MatriXX PT and MLSIC data. At the lateral margin, DR showed average agreement values within 0.3% of simulation at 100 Gy/s and fluctuations ∼10% at 15 Gy/s. LET spectra in the proximal, lateral, and distal margins had Bhattacharyya distances of <1.3%.ConclusionOur measurements with the MLSIC and Timepix3 detectors shown that the DR distributions for UHDR scenarios and LET spectra using USRe are in agreement with simulations. These results demonstrate that the methodology presented here can be used effectively for the experimental validation and QA of FLASH treatment plans.

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

Cited by 7 publications

References 74 publications

Development of a storage phosphor imaging system for proton pencil beam spot profile determination

Development of a storage phosphor imaging system for proton pencil beam spot profile determination

Calibration and time fading characterization of a new optically stimulated luminescence film dosimeter

Characterizing devices for validation of dose, dose rate, and LET in ultra high dose rate proton irradiations

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