Evaluation and mitigation of potential errors in radiochromic film dosimetry due to film curvature at scanning

Palmer, A.L.; Bradley, D.A.; Nisbet, Andrew

doi:10.1120/jacmp.v16i2.5141

Cited by 60 publications

(47 citation statements)

References 19 publications

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“…They signify an apparent increase in transmission as that distance becomes smaller in qualitative agreement with a recent finding. 46 Measurements were repeated with a selection of blue and neutral density filters. The results for the #1515 neutral density filter are characteristic for all examples and stand in high contrast to the EBT3 film as there is barely any change of the RGB response values by moving the filter toward the light.…”

Section: B Effect Of Film-light Source Distancementioning

confidence: 99%

Correcting scan‐to‐scan response variability for a radiochromic film‐based reference dosimetry system

Lewis¹,

Dević

2015

Medical Physics

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In the absence of measures to deal with the response irregularities, each factor the authors investigated could lead to dose uncertainty >2%. Those factors related to the film-to-light source distance could be particularly impactful since the authors observed many instances where the curl of film samples had the potential to cause dose uncertainty in excess of 5%. Two expedients will eliminate the uncertainties: a transparent sheet (preferably glass) placed over the scanned film keeps the film-to-light source distance constant, and an EBT3 reference film included in all scans provides correction factors for measured response values.

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Section: B Effect Of Film-light Source Distancementioning

confidence: 99%

Correcting scan‐to‐scan response variability for a radiochromic film‐based reference dosimetry system

Lewis¹,

Dević

2015

Medical Physics

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“…Some of them involve only the film: for example, the thickness variations of the active layer 2 , the change in film darkening as a function of post-irradiation time 3 , the influence of humidity and temperature 4,5 , the UV-induced polymerization 6 , etc. Some other uncertainties are a consequence of the interaction of the characteristics of both the film and scanner: for example, the lateral artifact 7,8 , Newton rings 9 , the dependency with the orientation of the film on the scanner bed 10 , the cross talk effect 8 , the dependency on film-to-light source distance 11,12 , etc. Finally, other uncertainties are intrinsic to the scanner: for example, noise 13,14 , the inter-scan variability of the scanner response 11 , warming-up of the lamp 15,16 , differences between color channels 17-20 , etc.…”

Section: Introductionmentioning

confidence: 99%

Grid patterns, spatial inter-scan variations and scanning reading repeatability in radiochromic film dosimetry

Méndez¹,

Šljivić²,

Hudej³

et al. 2016

Physica Medica

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Purpose: When comparing different scans of the same radiochromic film, several patterns can be observed. These patterns are caused by different sources of uncertainty, which affect the repeatability of the scanner. The purpose of this work was to study these uncertainties. Methods:The variance of the scanner noise, as a function of the pixel position, was studied for different resolutions. The inter-scan variability of the scanner response was analyzed taking into account spatial discrepancies. Finally, the distance between the position of the same point in different scans was examined.Results: The variance of noise follows periodical patterns in both axes, causing the grid patterns. These patterns were identified for resolutions of 50, 72 and 96 dpi, but not for 150 dpi. Specially recognizable is the sinusoidal shape with a period of 8.5 mm that is produced with 72 dpi. Inter-scan variations of the response caused systematic relative dose deviations larger than 1% in 5% of the red channel images, 9% of the green and 51% of the blue. No systematic deviation larger than 1% was found after applying response corrections. The initial positioning and the speed of the scanner lamp vary between scans.Conclusions: Three new sources of uncertainty, which influence radiochromic film dosimetry with flatbed scanners, have been identified and analyzed in this work: grid patterns, spatial inter-scan variations and scanning reading repeatability. A novel correction method is proposed, which mitigates spatial inter-scan variations caused by deviations in the autocalibration of the individual Charge Coupled Device detectors.

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“…All films were scanned in the central region of the scanner, away from the calibration area of the scanner. Typical natural curvature of film at scanning can give rise to a maximum height of 1 to 2 mm above scan plane and may introduce dose errors of 1% to 4% 18. To alleviate this error, a specialized film holder was constructed to make the films flush with the scanner plane.…”

Section: Methodsmentioning

confidence: 99%

Investigation of a source model for a new electronic brachytherapy tandem by film measurement

Martin

Sowards

Wang

2018

J Applied Clin Med Phys

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PurposeTo investigate the accuracy of a vendor‐supplied source model for a new Xoft Axxent 0‐degree titanium tandem by film measurement.MethodsWe measured the anisotropy factors at varying distances and angles from the tandem in water using radiochromic film (Gafchromic EBT3) and an Epson Perfection v750 desktop flatbed scanner (US Epson, Long Beach, CA). A 0‐degree tandem was placed vertically in a water phantom. Four pieces of film, each at varying depths, were positioned orthogonal to the longitudinal axis of the tandem for azimuthal anisotropy measurements. Polar anisotropy measurements were taken with the film aligned parallel to the tandem. An absolute dose calibration for the film was verified with a PTW 34013 Soft X‐Ray Chamber. The film measurements were analyzed using different color channels. The measured polar anisotropy for varying source positions was compared to the vendor's data. Azimuthal anisotropy was measured as a function of the radius and angle, and normalized to the mean value over all angles at the specified radius.ResultsThe azimuthal anisotropy of the tandem and source was found to be consistent for different positions along the tandem's longitudinal axis and at varying distances from the tandem. Absolute dose using a calibrated parallel plate chamber showed agreement to within 2% of expected TPS values. The custom tandem, which has a thicker tip than the wall, was attenuating the 50 kV photons more than expected, at the angles where the photons had more wall material to traverse. This discrepancy was verified at different distances from the tandem and with different measurement techniques. As distance increased, anisotropy values had better agreement.ConclusionsWe quantified the agreement between the measured and provided anisotropy factors for a new Xoft Axxent 0‐degree titanium tandem. Radiochromic film response at low kV energy was also investigated. Our results showed that vendor‐supplied TG‐43 values were appropriate for clinical use at majority of the angles. A rigorous quality assurance method for new electronic brachytherapy sources and applicators, along with complete knowledge of all dosimetric measuring tools, should be implemented for all parts of the verification and commissioning process.

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Evaluation and mitigation of potential errors in radiochromic film dosimetry due to film curvature at scanning

Cited by 60 publications

References 19 publications

Correcting scan‐to‐scan response variability for a radiochromic film‐based reference dosimetry system

Correcting scan‐to‐scan response variability for a radiochromic film‐based reference dosimetry system

Grid patterns, spatial inter-scan variations and scanning reading repeatability in radiochromic film dosimetry

Investigation of a source model for a new electronic brachytherapy tandem by film measurement

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