The suitable dose range for the calibration of EBT2 film by the PDD method with a comparison of two curve fitting algorithms

Lee

et al. 2015

Medical Physics

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Section: Methodsmentioning

confidence: 99%

Calibration of EBT2 film using a red‐channel PDD method in combination with a modified three‐channel technique

Lee

et al. 2015

Medical Physics

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“…The film was also oriented parallel to the central beam axis and the upper edge of the film was parallel to the gantry rotation axis, which is conventionally the Y-axis in the literature. [1426272833] To measure the reference dose, a 0.6 cc Farmer chamber was located at a depth of 31 cm, 10 cm thick backup plates were placed under the entire 30 cm × 30 cm × 30 cm phantom, and the source-surface-distance was set to 100 cm. The reference dose measurement using the chamber at depth 31 cm may not be necessary if the monthly dosimetry calibration was performed just before the film-dose calibration.…”

Section: Methodsmentioning

confidence: 99%

“…Several generations of Gafchromic film have been developed, but only EBT2 and EBT3 film are recommended by Ashland company for the verification of beam-modulated techniques[6] because spatial nonhomogeneity is corrected by the yellow marker dye,[5789101112] it has a lower sensitivity to the visible spectrum and it can be used for repeated scans. [1314] Using a matte polyester substrate to avoid the formation of Newton's rings,[15161718] EBT3 film has a similar composition for the active layer and dosimetric properties as EBT2[16] and either side of the film can be used. [19] The Ashland report states that the respective effective atomic numbers for EBT2 and EBT3 films are around 6.8 and 7.3, respectively, which is approximately equivalent to that for water.…”

Section: Introductionmentioning

confidence: 99%

Calibration of gafchromic EBT film using the Microtek ScanMaker 9800XL plus flatbed scanner with a modified one red-channel after three-channel method

Ding

et al. 2019

J Med Phys

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Purpose:Using the Microtek ScanMaker 9800XL Plus (9800XL+) flatbed scanner, a method is presented to accurately calibrate EBT film, which cannot be calibrated simply using a general three-channel method because of the nonhomogeneous scanning.Materials and Methods:Through the percentage-depth-dose method, 6-MV photon beams with two different monitor units were delivered to eight EBT2 films, each of which was tightly sandwiched in a 30-cm cubic polystyrene phantom and positioned parallel to the central axis of the beam. Before and after irradiation, all films were scanned using the Microtek 9800XL+ scanner and the pixel values (PVs) were measured along the central axis of the beam on the film and fitted to the corresponding depth doses. Before calibration, the irradiated film image was first modified using a template matrix, which was generated using the prescanned background images. Then, a modified one red-channel after three-channel method was used to calibrate the film.Results:Without a template matrix, the three-channel method cannot be used because the PVs do not correspond to a rational fitting form. Using the proposed method, the difference between the fitted dose and the delivered dose is <2%. The green channel, and not the red, is found to have the largest dynamic range.Conclusion:The proposed technique allows the use of the three-channel method to calibrate film using a Microtek 9800XL+ scanner.

“…Several generations of the Gafchromic film have been developed, but only EBT2 and EBT3 film models are recommended by Ashland for verifying all beam-modulated techniques [ 16 ]. This is because spatial nonhomogeneity is corrected by its yellow marker dye [ 15 , 17 – 22 ], so it is less sensitive to the visible spectrum, and it is available for repeated scans [ 23 , 24 ]. With the matte polyester substrate to avoid the formation of Newton's rings [ 25 – 28 ], the EBT3 film has active layer composition and dosimetric properties similar to EBT2 [ 26 ], with insignificant side dependence of the film [ 29 ].…”

Section: Introductionmentioning

confidence: 99%

“…With the matte polyester substrate to avoid the formation of Newton's rings [ 25 – 28 ], the EBT3 film has active layer composition and dosimetric properties similar to EBT2 [ 26 ], with insignificant side dependence of the film [ 29 ]. Based on the Ashland report, the effective atomic numbers of EBT2 and EBT3 films are around 6.8 and 7.3, which is approximately water equivalent, increasing their suitability for patient dosimetry [ 24 , 30 ].…”

Section: Introductionmentioning

confidence: 99%

Calibration of the EBT3 Gafchromic Film Using HNN Deep Learning

BioMed Research International

Yeh

et al. 2021

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To achieve a dose distribution conformal to the target volume while sparing normal tissues, intensity modulation with steep dose gradient is used for treatment planning. To successfully deliver such treatment, high spatial and dosimetric accuracy are crucial and need to be verified. With high 2D dosimetry resolution and a self-development property, the Ashland Inc. product EBT3 Gafchromic film is a widely used quality assurance tool designed especially for this. However, the film should be recalibrated each quarter due to the “aging effect,” and calibration uncertainties always exist between individual films even in the same lot. Recently, artificial neural networks (ANN) are applied to many fields. If a physicist can collect the calibration data, it could be accumulated to be a substantial ANN data input used for film calibration. We therefore use the Keras functional Application Program Interface to build a hierarchical neural network (HNN), with the inputs of net optical densities, pixel values, and inverse transmittances to reveal the delivered dose and train the neural network with deep learning. For comparison, the film dose calculated using red-channel net optical density with power function fitting was performed and taken as a conventional method. The results show that the percentage error of the film dose using the HNN method is less than 4% for the aging effect verification test and less than 4.5% for the intralot variation test; in contrast, the conventional method could yield errors higher than 10% and 7%, respectively. This HNN method to calibrate the EBT film could be further improved by adding training data or adjusting the HNN structure. The model could help physicists spend less calibration time and reduce film usage.