Dosimetric characterization and behaviour in small X-ray fields of a microchamber and a plastic scintillator detector

Pasquino, Massimo; Cutaia, C.; Radici, Lorenzo; Valzano, S.; Gino, Eva; Cavedon, Carlo; Stasi, M.

doi:10.1259/bjr.20160596

Cited by 16 publications

(16 citation statements)

References 43 publications

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“…The CLR factors for the W1 and W2 detector were determined at 22 C, which represents clinical measurements conditions. Our results take into account the CLR correction, which shows a linearly decreasing temperature response of the Exradin W2 and W1 detectors, which are in good agreement with Wooton et al and Carrasco et al 32 Pasquino et al 20 reported negligible field output factor variations due to irradiation geometries (parallel vs perpendicular) for different fields sizes (ranging from 0:6 Â 0:6 cm 2 to 10 Â 10 cm 2 at 10 cm depth) using the W1 Exradin scintillator. Our results show that the field output factor variations are within 3% for the 0:5 Â 0:5 cm 2 field size and 1% for the 1 Â 1 cm 2 and larger field sizes.…”

Section: Discussionsupporting

confidence: 91%

“…Pasquino et al . reported negligible field output factor variations due to irradiation geometries (parallel vs perpendicular) for different fields sizes (ranging from

0.6 \times 0.6 {cm}^{2}

10 \times 10 {cm}^{2}

at 10 cm depth) using the W1 Exradin scintillator.…”

Section: Discussionmentioning

confidence: 99%

“…Point‐wise PDD of the W1 is time consuming, but it is also identical to the PDD scanned with the W2, when enough time is given for adequate signal. We compared PDD values obtained with the W1 detector from the study of Pasquino et al . and the measured PDD with the W2 for the

1 \times 1 {cm}^{2}

and

3 \times 3 {cm}^{2}

field sizes at 2, 5, 10, and 20 cm depths.…”

Section: Discussionmentioning

confidence: 99%

“…The following tests were carried out as part of the characterization of the W2 detector for small field dosimetry: Beam dose profiles compared with Gafchromic film Field output factor comparisons with the Exradin W1 detector. Percent depth dose compared with the Exradin W1 detector from previous publications …”

Section: Methodsmentioning

confidence: 99%

“…Based on the data in TRS‐483 for the magnitude of the

k_{Q_{italicclin}, Q_{italicmsr}}^{f_{italicclin}, f_{italicmsr}}

factor, it can be concluded that the Exradin ® W1 (Standard Imaging, Madison, WI) PSD has a value near 1.0 and can be treated as an ideal detector without any correction. Although the W1 detector is an optimum choice for point dose measurements in small fields, it was not designed to be used with a scanning system. Point‐by‐point measurements for PDD, TMR, and OAR data collection are time consuming and prohibitive; thus, the W1 has limited applications.…”

Section: Introductionmentioning

confidence: 99%

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Characterization of the plastic scintillation detector Exradin W2 for small field dosimetry

Galavis

Holmes

et al. 2019

Medical Physics

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Purpose Small field dosimetry has been an active area of research for over a decade. It is now known that large dosimetric errors can be introduced if proper detectors or correction factors are not used. The International Atomic Energy Agency (IAEA) through the technical report series No. 483 provides guidelines for small field dosimetry procedures as well as correction factors for most detectors available in the market. The plastic scintillator detector (PSD) Exradin W1 has been found to have a correction factor close to unity; however, it is not designed for beam scanning. To overcome this limitation, the new PSD Exradin W2 has been developed to be used as a scanning as well as a relative dosimeter. Characterization of this detector in small field dosimetry is presented in this study. Methods A 6 MV beam from a Varian‐Edge linac was used to collect data for the characterization of a W2 detector. Cerenkov light ratio (CLR) is corrected through a separate new electrometer system that comes with the W2 detector. The parameters investigated include the dose and dose rate linearity, beam profiles, percent depth dose (PDD), field output factors, and temperature response. The results were compared with Gafchromic film (EBT‐3 film) for beam profiles. The field output factor and temperature response were compared to the Exradin W1 detector. Results The dose linearity measured with 600 MU/min dose rate showed minimal variations (<0.5%) even for small MU, and similar results were seen for dose rate linearity. The comparison of field output factors between the W2 and W1 showed small differences for various depth and field sizes. The temperature response showed small variation when the temperature was varied from 6∘C to 50∘C. The slope was −0.0017false/∘C and −0.0016false/∘C for the W2 and the W1 detector, respectively. The differences in profiles are 0.5% in umbra and penumbra region for 1×1cm2 field size when compared to the EBT‐3 film profile. Conclusions The W2 scintillator detector showed similar dosimetric and temperature properties to the W1 scintillator detector. The main advantage of the W2 detector among other plastic scintillators is the beam scanning capabilities that, combined with its correction factor of 1.0, make it an ideal detector for commissioning of SRS and SBRT techniques.

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Section: Discussionsupporting

confidence: 91%

“…Pasquino et al . reported negligible field output factor variations due to irradiation geometries (parallel vs perpendicular) for different fields sizes (ranging from

0.6 \times 0.6 {cm}^{2}

10 \times 10 {cm}^{2}

at 10 cm depth) using the W1 Exradin scintillator.…”

Section: Discussionmentioning

confidence: 99%

1 \times 1 {cm}^{2}

and

3 \times 3 {cm}^{2}

field sizes at 2, 5, 10, and 20 cm depths.…”

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

“…Based on the data in TRS‐483 for the magnitude of the

k_{Q_{italicclin}, Q_{italicmsr}}^{f_{italicclin}, f_{italicmsr}}

Section: Introductionmentioning

confidence: 99%

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Characterization of the plastic scintillation detector Exradin W2 for small field dosimetry

Galavis

Holmes

et al. 2019

Medical Physics

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Tomographic‐based 3D scintillation dosimetry using a three‐view plenoptic imaging system

et al. 2020

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To demonstrate the feasibility of a three-plenoptic camera projection, scintillation-based dosimetry system for measuring three-dimensional (3D) dose distributions of static photon radiation fields. Methods: Static x-ray photon beams were delivered to a cubic plastic scintillator volume embedded within acrylic blocks. For each beam, three orthogonal projections of the scintillating light emission were recorded using a multifocus plenoptic camera. Experimental 3D reconstructions of the light distribution were obtained using an iterative maximum likelihood-expectation maximization (ML-EM) algorithm. For this purpose, the elements of the system matrix representing the contribution of the scintillator volume voxels to the camera sensor pixels were calculated using optical design software. A reconstruction-specific correction was applied to light reconstructions to account for scintillating light imaged by the camera but not directly resulting from dose deposition. Cross beam profiles (CBPs) and percentage depth dose (PDD) curves were compared to treatment planning system data for square fields. Three-dimensional and 3D gamma analyses were performed for concave-shaped dose distributions and the Pearson correlation coefficient and reconstruction error were employed to assess the quality of the measured relative 3D dose distributions. Results: A full and accurate model of the plenoptic camera-based scintillation dosimetry system was implemented using the light ray tracing capabilities of optical design software. With this model, light distributions were successfully reconstructed over a volume of 60 9 60 9 60 mm 3 at a resolution of 2 mm. For relative 3D measurements of square radiation fields of 2 Â 2 cm 2 , 3 Â 3 cm 2 and 4 Â 4 cm 2 compared with treatment planning system reference distributions, the maximum rootmean-square error of the CBPs evaluated at two different depths was of 3.2%, 1.2%, and 1.1%, respectively; as for the corresponding linearly fitted PDDs of the square fields, the slopes of the reconstructed dose distributions overestimated those of the reference distributions by at most 0.2%/ cm. The 2D gamma passing rate with a criterion of 2%/2 mm for the concave-shaped photon field was of 61.6%, 66.1%, and 76.4% using one, two, and three plenoptic projections; the respective success rates become 77.1%, 87.5%, and 94.9% using a criterion of 3%/3 mm. The 3D correlation coefficient for the corresponding reconstructions was of 0.688, 0.905, and 0.976, respectively. Conclusions: Three-dimensional light distributions emitted from within a plastic scintillator volume were successfully recovered using optical design software to establish a complete tomographic model of a plenoptic camera-based prototype. The tomographic model can equivalently extend to dynamic dose delivery measurements, providing temporal resolution limited by the camera's exposure time. This feasibility study enables a simplified design-to-implementation process for volumetric scintillation dosimetry prototypes toward fully meeting the clinical n...

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Report of AAPM Task Group 155: Megavoltage photon beam dosimetry in small fields and non‐equilibrium conditions

et al. 2021

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Abbreviations: %dd(10) x , The photon component of the percent depth dose at 10 cm depth in water for a 10 cm 2 × 10 cm 2 field; L∕ w air , Restricted mass collision stopping power ratio of water to air; en ∕ , Spectrum-averaged mass energy-absorption coefficient; AAPM, American Association of Physicists in Medicine; CPE, Charged Particle Equilibrium; DLG, Dosimetric leaf gap; D f msr w,Q msr , Absorbed dose to water at the reference depth z ref in water in the absence of the detector in a field specified by f msr and beam quality Q msr .; f clin , Clinical (clin) non-reference radiation field; f msr , Machine-specific reference (msr) field; f ref , Reference field (ref) specified in dosimetry protocols for which the calibration coefficient of an ionization chamber in terms of absorbed dose to water is provided by a standards laboratory; FWHM, Full-width at half-maximum; GUM, Guide to the expression of Uncertainty in Measurements.; IAEA, International Atomic Energy Agency; ICRU, International Commission on Radiation Units and Measurements; IMRT, Intensity-modulated radiation therapy; k Q,Q 0 , The beam-quality correction factor, which corrects for the differences between the response of an ionization chamber in the reference beam of quality Q o used for calibrating the chamber and the beam of quality Q (defined as k Q . in TG-51 4 ); k f ref Q,Q 0 , Correction factor that accounts for the differences between the response of a detector in field f ref in a beam of quality Q and reference beam quality Q 0 as defined in TRS-483. 1 and Palmans et al 2 ; k fclin,fmsr Qclin,Q msr , The detector-specific correction factor that accounts for the difference between the responses of the detector in fields f clin in a beam of quality Q clin and in fields f msr in beam of quality Q msr as defined by Alfonso et al. 3 ; LCPE, Lateral charged particle equilibrium; M fmsr Qmsr , Detector reading in field f msr and beam quality Q msr corrected for influence of changes in pressure and temperature, incomplete charge collection, polarity effect and electrometer correction factor (TRS-483 1 ); MU, Monitor unit; N D,w,Q 0 , This is N D,w in TG-51, 4 and defined as the calibration coefficient in terms of absorbed dose to water for an ionization chamber at a reference beam of quality,Q 0 and field size f ref ; N f ref D,w,Q 0

show abstract

Dosimetric characterization and behaviour in small X-ray fields of a microchamber and a plastic scintillator detector

Cited by 16 publications

References 43 publications

Characterization of the plastic scintillation detector Exradin W2 for small field dosimetry

Characterization of the plastic scintillation detector Exradin W2 for small field dosimetry

Tomographic‐based 3D scintillation dosimetry using a three‐view plenoptic imaging system

Report of AAPM Task Group 155: Megavoltage photon beam dosimetry in small fields and non‐equilibrium conditions

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