Gafchromic EBT film dosimetry in proton beams

Zhao, Li; Das, Indra J.

doi:10.1088/0031-9155/55/18/5617

Cited by 29 publications

(64 citation statements)

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“…There is clearly dependence and for optimal results, a calibration film should be generated at the same depth as the measurement. This finding is in agreement with previous studies for depth calibration [39,40] or at the center of the SOBP [6,17,19]. However, the dependence for different ranges and modulations requires further investigation.…”

Section: Discussionsupporting

confidence: 92%

“…The particle energy of proton beam is variable with depth and could be losing energy continuously (lowest at Bragg peak and highest effect in depth dependence). The energy response is also dependent on the position of the Bragg peak [6]. …”

Section: Discussionmentioning

confidence: 99%

“…The parallel orientation was found to be superior as one can get an entire 2D data set from one single film. When using a single film piece positioned parallel to the proton beam axis, it is recommended to tilt the film plane at different degrees (1–5°) from the proton beam axis or the film can be kept in water [6,18]. The film had sufficient width so that water in the film would not cause additional perturbation.…”

Section: Discussionmentioning

confidence: 99%

“…Calibration films were irradiated at 18, 20, and 23 cm while the chamber array was irradiated at nearly identical depths of 18, 20 and 24 cm. The LET dependence of radiochromic films has been thoroughly investigated [6,18,22,26–33] and it has been established that the effect is highest for lower (< 11 MeV) proton energies [28]. However, for spot scanning beams, there may be a larger distribution of energies used to irradiate the PTV which could make accounting for LET corrections quite variable.…”

Section: Methodsmentioning

confidence: 99%

“…The SOBP is characterized by its range and width, or modulation [3]. Delivery of an SOBP has used different techniques including most commonly passive scattering [4,5] as well as uniform scanning [6,7]. …”

Section: Introductionmentioning

confidence: 99%

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Patient-Specific QA of Spot-Scanning Proton Beams Using Radiochromic Film

Chan¹,

Chen²,

Shi³

et al. 2017

IJMPCERO

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Radiochromic film for spot-scanning QA provides high spatial resolution and efficiency gains from one-shot irradiation for multiple depths. However, calibration can be a tedious procedure which may limit widespread use. Moreover, since there may be an energy dependence, which manifests as a depth dependence, this may require additional measurements for each patient. We present a one-scan protocol to simplify the procedure. A calibration using an EBT3 film, exposed by a 6-level step-wedge plan on a Proteus®PLUS proton system (IBA, Belgium), was performed at depths of 18, 20, 24cm using Plastic Water® (CIRS, Norfolk, VA). The calibration doses ranged from 65–250 cGy(RBE) (relative biological effectiveness) for proton energies of 170–200 MeV. A clinical prostate+nodes plan was used for validation. The planar doses at selected depths were measured with EBT3 films and analyzed using One-scan protocol (one-scan digitization of QA film and at least one film exposed to a known dose). The gamma passing rates, dose-difference maps, and profiles of 2D planar doses measured with EBT3 film and IBA MatriXX-PT, versus the RayStation TPS calculations were analyzed and compared. The EBT3 film measurement results matched well with the TPS calculation data with an average passing rate of ~95% for 2%/2mm and slightly lower passing rates were obtained from an ion chamber array detector. We were able to demonstrate that the use of a proton step-wedge provided clinically acceptable results and minimized variations between film-scanner orientation, inter-scan, and scanning conditions. Furthermore, for relative dosimetry (calibration is not done at the time of experiment) it could be derived from no more than two films exposed to known doses (one could be zero) for rescaling the master calibration curve at each depth. The sensitivity of the calibration to depth variations has been explored. One-scan protocol results appear to be comparable to that of the ion chamber array detector. The use of a proton step-wedge for calibration of EBT3 film potentially increases efficiency in patient-specific QA of proton beams.

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Section: Discussionsupporting

confidence: 92%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Patient-Specific QA of Spot-Scanning Proton Beams Using Radiochromic Film

Chan¹,

Chen²,

Shi³

et al. 2017

IJMPCERO

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Dosimetric verification of IMPT using a commercial heterogeneous phantom

Yasui

Toshito

Omachi

et al. 2019

J Applied Clin Med Phys

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The purpose of this study was to propose a verification method and results of intensity‐modulated proton therapy (IMPT), using a commercially available heterogeneous phantom. We used a simple simulated head and neck and prostate phantom. An ionization chamber and radiochromic film were used for measurements of absolute dose and relative dose distribution. The measured doses were compared with calculated doses using a treatment planning system. We defined the uncertainty of the measurement point of the ionization chamber due to the effective point of the chamber and mechanical setup error as 2 mm and estimated the dose variation base on a 2 mm error. We prepared a HU‐relative stopping power conversion table and fluence correction factor that were specific to the heterogeneous phantom. The fluence correction factor was determined as a function of depth and was obtained from the ratio of the doses in water and in the phantom at the same effective depths. In the simulated prostate plan, composite doses of measurements and calculations agreed within ±1.3% and the maximum local dose differences of each field were 10.0%. Composite doses in the simulated head and neck plan agreed within 4.0% and the maximum local dose difference for each field was 12.0%. The dose difference for each field came within 2% when taking the measurement uncertainty into consideration. In the composite plan, the maximum dose uncertainty was estimated as 4.0% in the simulated prostate plan and 5.8% in the simulated head and neck plan. Film measurements showed good agreement, with more than 92.5% of points passing a gamma value (3%/3 mm). From these results, the heterogeneous phantom should be useful for verification of IMPT by using a phantom‐specific HU‐relative stopping power conversion, fluence correction factor, and dose error estimation due to the effective point of the chamber.

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Monte Carlo simulations of EBT3 film dose deposition for percentage depth dose (PDD) curve evaluation

Robinson

Esplen

Wells

et al. 2020

J Applied Clin Med Phys

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Purpose: To use Monte Carlo (MC) calculations to evaluate the effects of Gafchromic EBT3 film orientation on percentage depth dose (PDD) curves. Methods: Dose deposition in films placed in a water phantom, and oriented either parallel or perpendicular with respect to beam axis, were simulated with MC and compared to PDDs scored in a homogenous water phantom. The effects of introducing 0.01-1.00 mm air gaps on each side of the film as well as a small 1°-3°tilt for film placed in parallel orientation were studied. PDDs scored based on two published EBT3 film compositions were compared. Three photon beam energies of 120 kVp, 220 kVp, and 6 MV and three field sizes between 1 × 1 and 5 × 5 cm 2 were considered. Experimental PDDs for a 6-MV 3 × 3 cm 2 beam were acquired. Results: PDD curves for films in perpendicular orientation more closely agreed to water PDDs than films placed in parallel orientation. The maximum difference between film and water PDD for films in parallel orientation was −12.9% for the 220 kVp beam. For the perpendicular film orientation, the maximum difference decreased to 5.7% for the 120 kVp beam. The inclusion of an air gap had the largest effect on the 6-MV 1 × 1 cm 2 beam, for which the dose in the buildup region was underestimated by 21.2% compared to the simulation with no air gap. A 2°film tilt decreased the difference between the parallel film and homogeneous water phantom PDDs from −5.0% to −0.5% for the 6 MV 3 × 3 cm 2 beam. The "newer" EBT3 film composition resulted in larger PDD discrepancies than the previous composition. Experimental film data qualitatively agreed with MC simulations. Conclusions: PDD measurements with films should either be performed with film in perpendicular orientation to the beam axis or in parallel orientation with a~2°tilt and no air gaps.

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Gafchromic EBT film dosimetry in proton beams

Abstract: We would like to correct a typographical error. In the last paragraph of Page N296, line 4, it should read 'α = 1.2269, β = −0.9446, γ = 1.1046 and δ = −0.004'.

Cited by 29 publications

References 0 publications

Patient-Specific QA of Spot-Scanning Proton Beams Using Radiochromic Film

Patient-Specific QA of Spot-Scanning Proton Beams Using Radiochromic Film

Dosimetric verification of IMPT using a commercial heterogeneous phantom

Monte Carlo simulations of EBT3 film dose deposition for percentage depth dose (PDD) curve evaluation

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