Characteristic of EBT-XD and EBT3 radiochromic film dosimetry for photon and proton beams

Khachonkham, Suphalak; Dreindl, R.; Heilemann, Gerd; Lechner, Wolfgang; Fuchs, H.; Palmans, Hugo; Georg, Dietmar; Kueß, Peter

doi:10.1088/1361-6560/aab1ee

Cited by 86 publications

(106 citation statements)

References 39 publications

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“…Films were positioned at the center of the scanner using a template to ensure a reproducible orientation. Although a small response change with the orientation has been reported for the EBT‐XD film model compared to the EBT3 model, in this study, the films were scanned in portrait mode. Images were acquired in transmission mode with RGB colors, 16 bits per color channel, all color corrections turned off, and spatial resolution of 72 dpi (0.35 mm × 0.35 mm pixel size).…”

Section: Methodsmentioning

confidence: 94%

“…The active layer of the EBT‐XD model is sandwiched between two matte polyester substrate each with 125 μm thickness, identical to that of the EBT3 model. There are several studies on the characterization and validation of the EBT‐XD films for radiotherapy dosimetry applications . These studies showed an improved performance of the EBT‐XD film over the EBT3 model for applications requiring doses greater than 10 Gy.…”

Section: Introductionmentioning

confidence: 99%

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Response characterization of EBT‐XD radiochromic films in megavoltage photon and electron beams

et al. 2019

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Purpose The purpose of this study was to investigate the beam quality dependence of the EBT‐XD radiochromic films for megavoltage photon and electron beam irradiations by studying their spectral response. Dose, dose rate, and interbatch dependencies were investigated as well. Methods EBT‐XD and EBT3 radiochromic films were cut into 5 cm2 × 5 cm2 pieces, placed between solid water phantoms, and irradiated with 6 and 15 MV photon beams, 6 and 10 MV flattening filter free photon beams, and 6 and 20 MeV electron beams at dose levels between 0.5 and 50 Gy. In order to measure the spectral response, the films were illuminated by a deuterium and tungsten‐halogen lamp and net absorption was measured in 400–800 nm spectral range using a fiber‐coupled optical spectrometer. Film samples were then analyzed using a flatbed scanner in the red, green, and blue channel to obtain the optical density of the films. Results The net absorption spectra of the EBT‐XD and EBT3 films showed two absorption bands centered at 635 and 585 nm, characteristic of the EBT model. However, for a given dose, the EBT‐XD films showed lower net absorbance compared to the EBT3 films. At a given dose level, the net absorption spectra and dose–response curves for EBT‐XD films showed only slight variations across various beam qualities. When a calibration curve obtained from a given beam quality is used to measure dose from films irradiated with other beam qualities, the maximum uncertainty in the calculated dose, in ranges 5–40 and 8–50 Gy for red and green channels, respectively, were ~3.1% and ~2.4%. Conclusions The response of the EBT‐XD films is dose rate independent but batch dependent. No significant beam quality dependence was observed in EBT‐XD films in the dose range up to 50 Gy.

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Section: Methodsmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Response characterization of EBT‐XD radiochromic films in megavoltage photon and electron beams

et al. 2019

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“…The 2D dose distribution was determined using Gafchromic EBT3 films (Ashland Advanced Materials, Bridgewater, NJ, USA) in a solid water phantom (Gammex/Sun Nuclear Corporation, Melbourne, Australia). The film was scanned using an Epson V700 scanner (Epson, Nagano, Japan) 24 h after irradiation . The resulting dose distribution was convolved with a disc‐shaped convolution kernel with 1.2 mm diameter to mimic the active volume of a PTW 60017 DiodeE detector (PTW, Freiburg, Germany).…”

Section: Methodsmentioning

confidence: 99%

An analytical formalism for the assessment of dose uncertainties due to positioning uncertainties

Lechner

Georg

2020

Medical Physics

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Purpose To present an analytical formalism for the in depth assessment of uncertainties of field output factors in small fields related to detector positioning based on dose profile measurements. Additionally, a procedure for the propagation of these uncertainties was developed. Methods Based on the assumption that one dimensional and two dimensional second‐order polynomial functions can be fitted to dose profiles of small photon beams, equations for the calculation of the expectation value, the variance, and the standard deviation were developed. The following fitting procedures of the dose profiles were considered: A one‐dimensional case (1D), a quasi two‐dimensional case (2Dq) based on independently measured line profiles and a full 2D case (2Df) which also considers cross‐correlations in a two‐dimensional dose distribution. A rectangular and a Gaussian probability density function (PDF) characterizing the probability of possible positions of the detector relative to the maximum dose were used. Uncertainty components such as the finite resolution of the scanning water phantom, the reproducibility of the determination of the position of the maximum dose, and the reproducibility of the collimator system were investigated. This formalism was tested in a 0.5 x 0.5 cm2 photon field where dose profiles were measured using a radiochromic film, a synthetic diamond detector, and an unshielded diode detector. Additionally, the dose distribution measured with the radiochromic film was convoluted with a convolution kernel mimicking the active volume of the unshielded diode. Results Analytic expressions for the calculation of uncertainties on field output factors were found for the 1D, the 2Dq, and the 2Df case. The uncertainty of the field output factor related to the relative position of the detector to the maximum dose increased quadratically with increasing limits of possible detector positions. Analysis of the radiochromic film showed that the 2Dq case gave a more conservative assessment of the uncertainty compared to the 2Df case with a difference of < 0.1%. The 2Dq case applied to the film measurements agreed well with the same approach as was applied to the unshielded diode. The investigated uncertainty components propagated to an uncertainty of the field output factors of 0.5% and 0.4% for the synthetic diamond and the unshielded diode, respectively. Additionally, the expectation value was lower than the maximum dose. The difference was 0.4% and 0.3% for the synthetic diamond and the unshielded diode, respectively. Conclusions The assessment of uncertainties of field output factors related to detector positioning is feasible using the proposed formalism. The 2Dq case is applicable when using online detectors. Accurate positioning in small fields is essential for accurate dosimetry as its related uncertainty increases quadratically. The observed drop of the expectation value needs to be considered in small field dosimetry.

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“…Further details about film handling and analysis can be obtained from previous results of our research group. 18,19,46 Besides the measurements with the homogeneous PMMA phantom, two heterogenous material configurations were investigated. Material (bone and tissue) slabs of 20 9 50 9 150 mm 3 were placed at the phantom entrance in two geometrical configurations: centrally and creating a lateral interface, see Fig.…”

Section: C2 Dose Distributionsmentioning

confidence: 99%

“…The energy-dependent response of Gafchromic EBT3 films makes their use for particle therapy more difficult compared to photon therapy. [16][17][18][19] For clinical proton beams, the dose obtained from films can be underestimated up to 20% in the Bragg peak region. 16,20,21 To correct for the LET quenching, several models are available in literature.…”

Section: Introductionmentioning

confidence: 99%

Benchmarking a GATE/Geant4 Monte Carlo model for proton beams in magnetic fields

et al. 2019

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Purpose: Magnetic resonance guidance in proton therapy (MRPT) is expected to improve its current performance. The combination of magnetic fields with clinical proton beam lines poses several challenges for dosimetry, treatment planning and dose delivery. Proton beams are deflected by magnetic fields causing considerable changes in beam trajectories and also a retraction of the Bragg peak positions. A proper prediction and compensation of these effects is essential to ensure accurate dose calculations. This work aims to develop and benchmark a Monte Carlo (MC) beam model for dose calculation of MRPT for static magnetic fields up to 1 T. Methods: Proton beam interactions with magnetic fields were simulated using the GATE/Geant4 toolkit. The transport of charged particle in custom 3D magnetic field maps was implemented for the first time in GATE. Validation experiments were done using a horizontal proton pencil beam scanning system with energies between 62.4 and 252.7 MeV and a large gap dipole magnet (B = 0-1 T), positioned at the isocenter and creating magnetic fields transverse to the beam direction. Dose was measured with Gafchromic EBT3 films within a homogeneous PMMA phantom without and with bone and tissue equivalent material slab inserts. Linear energy transfer (LET) quenching of EBT3 films was corrected using a linear model on dose-averaged LET method to ensure a realistic dosimetric comparison between simulations and experiments. Planar dose distributions were measured with the films in two different configurations: parallel and transverse to the beam direction using single energy fields and spread-out Bragg peaks. The MC model was benchmarked against lateral deflections and spot sizes in air of single beams measured with a Lynx PT detector, as well as dose distributions using EBT3 films. Experimental and calculated dose distributions were compared to test the accuracy of the model. Results: Measured proton beam deflections in air at distances of 465, 665, and 1155 mm behind the isocenter after passing the magnetic field region agreed with MC-predicted values within 4 mm. Differences between calculated and measured beam full width at half maximum (FWHM) were lower than 2 mm. For the homogeneous phantom, measured and simulated in-depth dose profiles showed range and average dose differences below 0.2 mm and 1.2%, respectively. Simulated central beam positions and widths differed <1 mm to the measurements with films. For both heterogenous phantoms, differences within 1 mm between measured and simulated central beam positions and widths were obtained, confirming a good agreement of the MC model. Conclusions: A GATE/Geant4 beam model for protons interacting with magnetic fields up to 1 T was developed and benchmarked to experimental data. For the first time, the GATE/Geant4 model was successfully validated not only for single energy beams, but for SOBP, in homogeneous and heterogeneous phantoms. EBT3 film dosimetry demonstrated to be a powerful dosimetric tool, once the film response function is LET corrected,...

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Characteristic of EBT-XD and EBT3 radiochromic film dosimetry for photon and proton beams

Cited by 86 publications

References 39 publications

Response characterization of EBT‐XD radiochromic films in megavoltage photon and electron beams

Response characterization of EBT‐XD radiochromic films in megavoltage photon and electron beams

An analytical formalism for the assessment of dose uncertainties due to positioning uncertainties

Benchmarking a GATE/Geant4 Monte Carlo model for proton beams in magnetic fields

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