Design and implementation of a film dosimetry audit tool for comparison of planned and delivered dose distributions in high dose rate (HDR) brachytherapy

Palmer, A.L.; Lee, Chris; Ratcliffe, A J; Bradley, D.A.; Nisbet, Andrew

doi:10.1088/0031-9155/58/19/6623

Cited by 40 publications

(44 citation statements)

References 51 publications

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“…The resulting film dose range was 2 to 13 Gy. The film was positioned in a liquid water tank for irradiation using the BRAD audit phantom, as described by Palmer et al (15) The film was scanned flat under a glass compression plate and also scanned allowing the natural curve in the film to be exhibited, which gave a maximum 1.5 mm height at the center of the film while in contact with the scanner plate at two opposite edges, as shown in Fig. 1.…”

Section: Methodsmentioning

confidence: 99%

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

Palmer

Bradley

Nisbet

2015

J Applied Clin Med Phys

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This work considers a previously overlooked uncertainty present in film dosimetry which results from moderate curvature of films during the scanning process. Small film samples are particularly susceptible to film curling which may be undetected or deemed insignificant. In this study, we consider test cases with controlled induced curvature of film and with film raised horizontally above the scanner plate. We also evaluate the difference in scans of a film irradiated with a typical brachytherapy dose distribution with the film naturally curved and with the film held flat on the scanner. Typical naturally occurring curvature of film at scanning, giving rise to a maximum height 1 to 2 mm above the scan plane, may introduce dose errors of 1% to 4%, and considerably reduce gamma evaluation passing rates when comparing film‐measured doses with treatment planning system‐calculated dose distributions, a common application of film dosimetry in radiotherapy. The use of a triple‐channel dosimetry algorithm appeared to mitigate the error due to film curvature compared to conventional single‐channel film dosimetry. The change in pixel value and calibrated reported dose with film curling or height above the scanner plate may be due to variations in illumination characteristics, optical disturbances, or a Callier‐type effect. There is a clear requirement for physically flat films at scanning to avoid the introduction of a substantial error source in film dosimetry. Particularly for small film samples, a compression glass plate above the film is recommended to ensure flat‐film scanning. This effect has been overlooked to date in the literature.PACS numbers: 87.55.Qr, 87.56.bg, 87.55.km

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Section: Methodsmentioning

confidence: 99%

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

Palmer

Bradley

Nisbet

2015

J Applied Clin Med Phys

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“…Eight peer-reviewed journal publications were obtained that presented results of fully completed audits or pilot audits at several centres, involving dosimetric measurement, 18,[37][38][39][40][41][42][43] and one concerned with a geometric applicator reconstruction audit. 44 Two more journal publications presented methodologies for brachytherapy audit currently in progress, 45,46 and the authors are aware of another two audits currently in progress in the UK that are not yet described in the literature: a well-type chamber intercomparison and an alanine dosimetry phantom measurement of source strength, discussed later. Each of these above audits deals with afterloading equipment.…”

Section: Dosimetric Audits In Brachytherapymentioning

confidence: 99%

“…This is a more complex measurement challenge that might result in increased uncertainty, with a lack of specificity of any errors, but at the benefit of a more "clinically realistic" dosimetric audit. Palmer et al 45 were the first to report on the design and implementation of a pilot "end-to-end" system audit for brachytherapy, involving radiochromic film measurement of dose distribution around clinical treatment applicators with comparison with treatment planning system calculations. The test object consisted of a near full-scatter water tank with applicator and film supports constructed of Solid Water®, accommodating any typical HDR/PDR cervix treatment applicator.…”

Section: Dosimetric Audits In Brachytherapymentioning

confidence: 99%

“…Typical clinical dwell patterns and prescription doses were used for the audit. The results from just two pilot audits are presented in the article by Palmer et al, 45 using Co-60 and Ir-192 HDR sources, with comparison of planned and delivered dose distributions having the mean g passing rate of 98.6% at 3% local normalization and 3 mm criteria, and the mean distance to agreement at Point A of 1.2 mm. The phantom is currently being used (2013)(2014) to audit all brachytherapy centres in the UK.…”

Section: Dosimetric Audits In Brachytherapymentioning

confidence: 99%

“…While previous concerns of source calibration might now essentially be resolved, which should lead to reduced uncertainty in determination of source strength, it is important not to abandon audit checks of this fundamental parameter, but it does enable a shift in focus to more complex areas for audit. 45 As discussed earlier, dosimetric measurements in clinical brachytherapy situations are problematic and measurement uncertainties might increase as we move closer to the clinical treatment situation. In the future, the gold-standard dosimetric audit may be verification by in vivo measurement and will certainly include an "end-to-end" system approach.…”

Section: The Future Of Dosimetric Audits In Brachytherapymentioning

confidence: 99%

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Dosimetric audit in brachytherapy

Palmer¹,

Bradley²,

Nisbet³

2014

BJR

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Dosimetric audit is required for the improvement of patient safety in radiotherapy and to aid optimization of treatment. The reassurance that treatment is being delivered in line with accepted standards, that delivered doses are as prescribed and that quality improvement is enabled is as essential for brachytherapy as it is for the more commonly audited external beam radiotherapy. Dose measurement in brachytherapy is challenging owing to steep dose gradients and small scales, especially in the context of an audit. Several different approaches have been taken for audit measurement to date: thimble and well-type ionization chambers, thermoluminescent detectors, optically stimulated luminescence detectors, radiochromic film and alanine. In this work, we review all of the dosimetric brachytherapy audits that have been conducted in recent years, look at current audits in progress and propose required directions for brachytherapy dosimetric audit in the future. The concern over accurate source strength measurement may be essentially resolved with modern equipment and calibration methods, but brachytherapy is a rapidly developing field and dosimetric audit must keep pace.

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Evaluating dosimetric accuracy of the 6 MV calibration on EBT3 film in the use of Ir‐192 high dose rate brachytherapy

Huang

Gaballa

Chang

2022

J Applied Clin Med Phys

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To evaluate the dosimetric accuracy of EBT3 film calibrated with a 6 MV beam for high dose rate brachytherapy and propose a novel method for direct film calibration with an Ir-192 source. Methods: The 6 MV calibration was performed in water on a linear accelerator (linac). The Ir-192 calibration was accomplished by irradiating the film wrapped around a cylinder applicator with an Ir-192 source. All films were scanned 1-day post-irradiation to acquire calibration curves for all three (red, blue, and green) channels. The Ir-192 calibration films were also used for single-dose comparison. Moreover, an independent test film under a H.A.M. applicator was irradiated and the 2D dose distribution was obtained separately for each calibration using the red channel data. Gamma analysis and point-by-point profile comparison were performed to evaluate the performance of both calibrations. The uncertainty budget for each calibration system was analyzed. Results: The red channel had the best performance for both calibration systems in the single-dose comparison. We found a significant 4.89% difference from the reference for doses <250 cGy using the 6 MV calibration, while the difference was only 0.87% for doses >600 cGy. Gamma analysis of the 2D dose distribution showed the Ir-192 calibration had a higher passing rate of 91.9% for the 1 mm/2% criterion, compared to 83.5% for the 6 MV calibration. Most failing points were in the low-dose region (<200 cGy). The point-by-point profile comparison reported a discrepancy of 2%-3.6% between the Ir-192 and 6 MV calibrations in this low-dose region. The linac-and Ir-192-based dosimetry systems had an uncertainty of 4.1% (k = 2) and 5.66% (k = 2), respectively. Conclusions: Direct calibration of EBT3 films with an Ir-192 source is feasible and reliable, while the dosimetric accuracy of 6 MV calibration depends on the dose range. The Ir-192 calibration should be used when the measurement dose range is below 250 cGy.

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Design and implementation of a film dosimetry audit tool for comparison of planned and delivered dose distributions in high dose rate (HDR) brachytherapy

Cited by 40 publications

References 51 publications

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

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

Dosimetric audit in brachytherapy

Evaluating dosimetric accuracy of the 6 MV calibration on EBT3 film in the use of Ir‐192 high dose rate brachytherapy

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