On the re-calibration process in radiochromic film dosimetry

Ruiz-Morales, Carmen; Vera-Sánchez, Juan Antonio; González‐López, Antonio

doi:10.1016/j.ejmp.2017.08.013

Cited by 14 publications

(31 citation statements)

References 20 publications

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“…In this study, only results from the 12000XL scanner were reported since other studies already addressed xenon fluorescent lamp‐based scanners . The changes seen in Fig.…”

Section: Discussionmentioning

confidence: 99%

“…This amount of variation was not seen when using any of the response functions included in this study for the 12000XL scanner. For this reason the recalibration protocols have surfaced in the literature . Ruiz‐Morales et al reported the variability of 20 scans from the 10000XL scanner and showed that recalibration methods accounted for it (<0.2% variation after the 20th scan) while control film piece protocol could not (at all color channels), where the maximum deviation was 1% in the green channel.…”

Section: Discussionmentioning

confidence: 99%

“…The stability of the RCF dosimetry system over longer periods of time is definitely a desirable feature. However, the inaccuracies seen in scanner variability prompted the use of recalibration protocols to seek more reliable dosimetry systems. In this study,

n P V_{italicRGB}

was shown to provide the same dosimetric performance seen during calibration, at later time points (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…Most of the empirical models were shown to be accurate when used in conditions similar to the calibration conditions; however, possible changes in the scanner‐film states may lead into significant inaccuracies if not accounted for. This in turn lead into the introduction of recalibration protocols which took these changes into account but with the caveat that they require extra irradiation(s) of reference dose(s) to rescale the calibration curve.…”

Section: Introductionmentioning

confidence: 99%

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Dose–response linearization in radiochromic film dosimetry based on multichannel normalized pixel value with an integrated spectral correction for scanner response variations

et al. 2019

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Purpose: To introduce a model that reproducibly linearizes the response from radiochromic film (RCF) dosimetry systems at extended dose range. To introduce a correction method, generated from the same scanned images, which corrects for scanner temporal response variation and scanner bed inhomogeneity. Methods: Six calibration curves were established for different lot numbers of EBT3 GAFCHRO-MIC TM film model based on four EPSON scanners [10000XL (2 units), 11000XL, 12000XL] at three different centers. These films were calibrated in terms of absorbed dose to water based on TG51 protocol or TRS398 with dose ranges up to 40 Gy. The film response was defined in terms of a proposed normalized pixel value (nPV RGB ) as a summation of first-order equations based on information from red, green, and blue channels. The fitting parameters of these equations are chosen in a way that makes the film response equal to dose at the time of calibration. An integrated set of correction factors (one per color channel) was also introduced. These factors account for the spatial and temporal changes in scanning states during calibration and measurements. The combination of nPV RGB and this "fingerprint" correction formed the basis of this new protocol and it was tested against net optical density (netOD X¼R;G;B ) single-channel dosimetry in terms of accuracy, precision, scanner response variability, scanner bed inhomogeneity, noise, and long-term stability. Results: Incorporating multichannel features (RGB) into the normalized pixel value produced linear response to absorbed dose (slope of 1) in all six RCF dosimetry systems considered in this study. The "fingerprint" correction factors of each of these six systems displayed unique patterns at the time of calibration. The application of nPV RGB to all of these six systems could achieve a level of accuracy of AE 2.0% in the dose range of interest within modeled uncertainty level of 2.0%-3.0% depending on the dose level. Consistent positioning of control and measurement film pieces and integrating the multichannel correction into the response function formalism mitigated possible scanner response variations of as much as AE 10% at lower doses and scanner bed inhomogeneity of AE 8% to the established level of uncertainty at the time of calibration. The system was also able to maintain the same level of accuracy after 3 and 6 months post calibration.Conclusions: Combining response linearity with the integrated correction for scanner response variation lead to a sustainable and practical RCF dosimetry system that mitigated systematic response shifts and it has the potential to reduce errors in reporting relative information from the film response.

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“…In this study, only results from the 12000XL scanner were reported since other studies already addressed xenon fluorescent lamp‐based scanners . The changes seen in Fig.…”

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

n P V_{italicRGB}

was shown to provide the same dosimetric performance seen during calibration, at later time points (Fig.…”

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Dose–response linearization in radiochromic film dosimetry based on multichannel normalized pixel value with an integrated spectral correction for scanner response variations

et al. 2019

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“…On the other hand, the dosimetry system composed of radiochromic films and a flatbed scanner suffers from several sources of uncertainty, which can affect the film (e.g., differences in the active layer thickness 9 , evolution of film darkening with post-irradiation time 10,11 , dependency on humidity and temperature 12 , noncatalytic and ultraviolet-catalyzed polymerization 13 , scratches), the scanner (e.g., the warming-up of the lamp 14,15 , inter-scan variations 16,17 , noise 18,19 , dust), or the interaction between film and scanner (e.g., the lateral artifact [20][21][22] , the dependency on the orientation of the film on the scanner bed 23 , the dependency on film-to-light source distance 16, 24 , Newton rings 25 , the cross talk effect 21 ). Film handling and scanning protocols 8,18 , corrections 16,17, [26][27][28][29] and multichannel dosimetry methods [30][31][32][33] have been developed to reduce uncertainties and deliver precise and accurate doses 34,35 .…”

Section: Introductionmentioning

confidence: 99%

The Multigaussian method: a new approach to mitigating spatial heterogeneities with multichannel radiochromic film dosimetry

Méndez¹,

Polšak²,

Hudej³

et al. 2018

Phys. Med. Biol.

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The main objective of multichannel radiochromic film dosimetry methods is to correct, or at least mitigate, spatial heterogeneities in the film-scanner response, especially variations in the active layer thickness. To this end, films can also be scanned prior to irradiation. In this study, the abilities of various single channel and multichannel methods to reduce spatial heterogeneities, with and without scanning before irradiation, were tested. Red, green and blue single channel models, two additive channel independent perturbation (CHIP) models and two multiplicative CHIP models were compared with the Multigaussian method. The Multigaussian method is a new approach to multichannel dosimetry, based on experimental findings. It assumes that the probability density function of the response vector formed by the pixel values of the different color channels, including irradiated and non-irradiated scans, follows a multivariate Gaussian distribution. The Multigaussian method provided more accurate doses than the other models under comparison, especially when incorporating the information of the film prior to irradiation. The relative dose differences between reference doses measured with MatriXX and film doses were examined. After applying inter-scan and lateral corrections, the lowest mean absolute errors were 0.8% and 1.0% for the Multigaussian method with and without the information of the scan before irradiation, respectively. Followed by the uniform multiplicative CHIP and red single channel models, using pixel values and net optical density, respectively, both with 1.1%.

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A method for time‐independent film dosimetry: Can we obtain accurate patient‐specific QA results at any time postirradiation?

Dunn

Godwin

Hellyer

et al. 2022

J Applied Clin Med Phys

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Aim The aim of this work was twofold. (1) To investigate and present a comparison between EBT3 and EBT‐XD in terms of postirradiation color changes. (2) Create an automated workflow to allow radiochromic film (EBT3/XD) to be scanned and converted to dose accurately at any postirradiation time. Materials and Methods Ten GafChromic EBT‐XD calibration films were exposed in 2 Gy increments up to 18 Gy. Calibrates were then scanned at 5‐min intervals postirradiation over 24 h using an AutoHotKey script, resulting in 288 TIFF images. Following the 24‐h scanning period, a MATLAB script was used to automatically read the tiff images and create a series of 288 calibration curves distinct in time which is termed as the “Temporal Calibration Model” (TCM). The model is saved as a series of polynomial fit coefficients to net optical density as a function of dose, timestamped in 5‐min increments. Ten patient‐specific film measurements (5 × EBT‐XD and 5 × EBT3) were then carried out and scanned using the same 5‐min scan intervals from 5 min postirradiation to 24 h postirradiation. The TCM was then automatically applied using eFilmQA software to convert the patient‐specific QA films to dose by applying the relevant calibration curve from the TCM, corresponding to the arbitrary postirradiation time that the film was scanned. Each dose plane at postirradiation scan intervals of 5 min up to 20 h was then compared to the ground‐truth dose plane using gamma analysis. Results Gamma pass rates using the TCM at time t, normalized to the pass rate after 20 h postirradiation, were found to have a maximum coefficient of variation of 3% over any postirradiation time. Conversely, not using the TCM resulted in coefficients of variation of up to 39%. Clinical implementation of this method showed an average accuracy of 2.8% when comparing the clinical result to the TCM result. Conclusions We have developed a methodology that allows radiochromic film to be accurately used as a dosimeter at any arbitrary scan postirradiation time, whereas previously, waiting periods of 16–24 h before readout were needed to ensure the postirradiation changes had stabilized. The creation of a TCM can enable results from radiochromic film measurements to be obtained quickly postirradiation. Using a conventional single calibration curve generated at 20 h postirradiation can result in gamma pass‐rate difference of up to 75% for measurement films scanned at a much shorter postirradiation time.

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On the re-calibration process in radiochromic film dosimetry

Cited by 14 publications

References 20 publications

Dose–response linearization in radiochromic film dosimetry based on multichannel normalized pixel value with an integrated spectral correction for scanner response variations

Dose–response linearization in radiochromic film dosimetry based on multichannel normalized pixel value with an integrated spectral correction for scanner response variations

The Multigaussian method: a new approach to mitigating spatial heterogeneities with multichannel radiochromic film dosimetry

A method for time‐independent film dosimetry: Can we obtain accurate patient‐specific QA results at any time postirradiation?

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