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Original Article

Progress in Medical Physics 2022; 33(4): 158-163

Published online December 31, 2022 https://doi.org/10.14316/pmp.2022.33.4.158

Copyright © Korean Society of Medical Physics.

Determination of Absorbed Dose for Gafchromic EBT3 Film Using Texture Analysis of Scanning Electron Microscopy Images: A Feasibility Study

So-Yeon Park

Department of Radiation Oncology, Veterans Health Service Medical Center, Seoul, Korea

Correspondence to:So-Yeon Park
(vsoyounv@gmail.com)
Tel: 82-2-2225-4648
Fax:82-2-2225-4640

Received: November 28, 2022; Revised: December 19, 2022; Accepted: December 20, 2022

This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Purpose: We subjected scanning electron microscopic (SEM) images of the active layer of EBT3 film to texture analysis to determine the dose-response curve.
Methods: Uncoated Gafchromic EBT3 films were prepared for direct surface SEM scanning. Absorbed doses of 0–20 Gy were delivered to the film’s surface using a 6 MV TrueBeam STx photon beam. The film’s surface was scanned using a SEM under 100× and 3,000× magnification. Four textural features (Homogeneity, Correlation, Contrast, and Energy) were calculated based on the gray level co-occurrence matrix (GLCM) using the SEM images corresponding to each dose. We used R-square to evaluate the linear relationship between delivered doses and textural features of the film’s surface.
Results: C orrelation r esulted i n h igher l inearity a nd d ose-response c urve s ensitivity t han Homogeneity, Contrast, or Energy. The R-square value was 0.964 for correlation using 3,000× magnified SEM images with 9-pixel offsets. Dose verification was used to determine the difference between the prescribed and measured doses for 0, 5, 10, 15, and 20 Gy as 0.09, 1.96, −2.29, 0.17, and 0.08 Gy, respectively.
Conclusions: Texture analysis can be used to accurately convert microscopic structural changes to the EBT3 film’s surface into absorbed doses. Our proposed method is feasible and may improve the accuracy of film dosimetry used to protect patients from excess radiation exposure.

KeywordsFilm dosimetry, Gafchromic film, Texture analysis, Scanning electron microscopy

Radiochromic film was first developed in 2004 and is the most commonly used dosimetric radiotherapy tool [1]. Gafchromic EBT3 films (Ashland Inc., Wayne, NJ, USA), currently the most widely used radiochromic films, feature high spatial resolution, tissue equivalence characteristics, and the advantage of two-dimensional (2D) measurements [2,3]. These films are also used for quality assurance and to determine in vivo dosimetry when administering advanced radiotherapy techniques like intensity-modulated radiation therapy and volumetric-modulated arc therapy [3-7].

Radiation doses to the EBT3 film surface are determined by obtaining scanner images of the film’s opacity before and after radiation exposure. Radiation dose values are then derived from red-green-blue (RGB) image values which mathematically represents color information using three or four different color parameters. This step is followed by color quantification standardization. However, procedural variables like active layer non-uniformities, scanning non-uniformities, and film scan angle can affect dosimetric accuracy [1,8-11].

Various institutions have evaluated the overall dosimetry uncertainty of EBT3 films according to RGB configurations within various measurement and scanning environments. These experiments revealed the dosimetric uncertainty estimates of 3.2% for R, 4.9% for G, and 5.2% for B channels [12]. Another study proposed a calibration curve that used the triple-channel analysis method to reduce dosimetric uncertainty and relative standard deviation and improve dosimetric accuracy [13,14]. These efforts underscore the importance of accurately measuring radiation doses to EBT3 film; relevant research is ongoing.

Texture analysis quantifies pixels within 2D images that cannot be recognized with the naked eye [15-17]. Texture analysis is used for radiomic analysis of medical images. For example, a patient’s prognosis can be determined using texture analysis. 2D images can be quantified through texture analysis and used for dose measurement [18]. Shih et al. obtained polymer gel surface images using scanning electron microscopy (SEM) after application of various (5, 10, 15, and 20 Gy) radiation doses. The researchers analyzed four textural features to determine potential correlations with the delivered doses [19]. Using the dose calibration curve, the authors found differences in delivered doses of −7.60% for 5 Gy, 5.80% for 10 Gy, 2.53% for 15 Gy, and −0.95% for 20 Gy [19].

Images of the film’s active layer were obtained using SEM after irradiation with various radiation doses. Each SEM image was subjected to texture analysis to determine its relevant features. We additionally determined the dose calibration curve between the calculated and delivered dose values to evaluate the dose calibration curve’s accuracy.

1. Radiochromic EBT3 film

The EBT3 film consists of a 28-μm-thick active layer that reacts to radiation and a 125-μm-thick transparent polyester substrate layer that protects the active layer. The substrate layer is positioned above and below the active layer to reduce damage and interference by external ultraviolet (UV) and normal lights. The active layer in the EBT3 film contains yellow-colored, radiation-sensitive chemicals that become opaque after polymerization from radiation exposure. The adjusted opacity value obtained from each of the RGB channels is used to calculate optical density, which strongly correlates with radiation dose. We purchased EBT3 film samples with the upper substrate layer removed to directly image the active layer’s surface (Fig. 1). Because EBT3 film is sensitive to UV and general light, the samples were stored in a dark room except during irradiation and the acquisition of SEM images.

Figure 1.Depiction of Gafchromic EBT3 film’s surface structure. (a) Laminated EBT3 film. (b) Unlaminated EBT3 film.

2. Irradiation

All EBT3 film samples were cut into 1×1 cm2 pieces and placed on a 5-cm thick solid water phantom and covered with oil paper to prepare for irradiation and prevent scratching of the active layer’s surface. A 1.5-cm thick solid water phantom was placed on the EBT3 film’s surface. A 100-cm source-to-surface distance and 10×10 cm2 irradiation field were established. After dose calidation for 6 MV photon rays was performed according to the American Association of Physicians in Medicine’s Task Group 51 protocol, the samples were irradiated using 6 MV photon rays produced by the TrueBeam STx (Varian Medical Systems, Palo Alto, CA, USA) [20] to ensure accurate dose delivery. Radiation doses of 0, 5, 10, 15, and 20 Gy were administered over five sets, using one set of four films. The irradiated films were placed in a dark room for more than 24 hours for self-development.

3. SEM scanning

To obtain the SEM images, we coated the 4-nm-thick EBT3 surfaces with iridium to amplify the electron signals. SEM SNE-4500M (SEC, Suwon, Korea) was for SEM image acquisition in environments of 10 kV and 100 μA. Four measurement points were designated uniformly on each film sample and each measurement point was examined under 100× and 3,000× magnification.

4. Calculation of textural parameters

Texture analysis used a gray level co-occurrence matrix (GLCM) to determine between-pixel relationships. When determining GLCM, the between-pixel distance “d” was changed from 1 to 30, and we used between-pixel angles “θ” of 0°, 45°, 90°, and 135°. The quantization level (Ng) was 64, the level most frequently used for texture analysis. Using GLCM, the four most representative textural features—Entropy, Contrast, Energy, and Homogeneity—were calculated according to the following equations:

Entropy= i=1 Ngj=1Ngp i, jlog(p i,j), 
Contrast= i=1 Ngj=1Ng ij2p i, j,
Energy= i=1 Ngj=1Ngp i, j2 ,
Homogeneity= i=1 Ngj=1Ng1 1+ ij2 p i, j,

here, i and j refer to the horizontal and vertical axis coordinates of GLCM, respectively. The spatial dependence matrix of GLCM is denoted by p(i, j), indicating the probability of a between-pixel relationship for each (i, j).

Four textural features were obtained to determine the distances and angles between pixels. The average between-pixel angle was chosen as the representative value. In other words, for each surface image, we obtained representative values for each of the four textural analysis parameters.

5. Determination of dose calibration curves and statistical analysis

We performed a linear regression analysis to determine the correlation between the textural features and delivered doses and calculated maximum R-squared values to evaluate the correlations between doses and each textural parameter.

Fig. 2 depicts a surface EBT3 film image obtained using SEM. The images that were magnified 3,000× represented the active layer’s structural molecules more clearly than those magnified 100×. As the delivered dose increased, the active layer’s surface became smoother through molecular polymerization.

Figure 2.An EBT3 film surface image obtained using scanning electron microscopic (SEM). Each measurement point is visualized under 100× and 3,000× magnification and absolute radiation doses of 0, 5, 10, 15, and 20 Gy.

Fig. 3 depicts the correlation between textural features and radiation doses as a function of pixel distance. Under 100× magnification, Contrast and Homogeneity had R-squared values of ≥0.5 for all between-pixel distances. For Homogeneity (d=1), the maximum R-squared value was 0.761. Using 3,000× magnification, the R-squared value was ≥0.5 for all between-pixel distances except for the correlation with a d=1–4. Correlation (d=9) produced an R-squared value of 0.964.

Figure 3.The maximum coefficient of determination value based on the between-pixel distance and the textural features obtained following irradiation and under (a) 100× and (b) 3,000× surface magnification.

Fig. 4 depicts the dose calibration curve obtained using correlation (d=9) under 3,000× magnification and with the highest maximum coefficient of determination value. When the radiation dose was calculated based on the dose correction curve of the correlation (d=9), the differences between the actual delivered radiation dose values and calculated dose values were 0.09, 1.96, −2.29, 0.17, and 0.08 Gy for 0, 5, 10, 15, and 20 Gy, respectively.

Figure 4.Correlation curve of the parameter of Correlation (d=9) for the EBT3 film’s surface under 3,000× magnification and various radiation doses.

We performed dosimetry on EBT3 film samples using SEM and texture analysis of the samples’ surfaces. SEM was used to visualize the microscopic molecular structure of the film’s active layer. Texture analysis was used to quantify changes in molecular structure caused by radiation. Changes to the film’s surface texture were highly correlated with delivered radiation doses.

Shin et al. [19] reported gradual surface smoothing with delivery of increasingly high radiation doses. These results are consistent with our findings. Arjomandy et al. [21] found that delivering 2–10 Gy doses to EBT2 film surfaces reduced surface roughness at higher doses. Microscopically, the reaction between the radiation particles and the active layer’s chemical molecules elicits polymerization. Volotskova et al. found changes to molecular structure after EBT3 and EBT-XD films were irradiated and then analyzed using SEM surface imaging [22]. The authors found no reduction in surface roughness, unlike our results. Polymerization caused the active surface layer’s needle-shaped structure to elongate as a result of radiation exposure [22].

Because we only used SEM to analyze the EBT3 surface images, surface impurities or defects could have affected our results. However, we avoided using film samples with impurities or defects at the measurement points when we acquired our SEM images. Additionally, SEM uses high-voltage, accelerated electrons that might deliver excess radiation to an object’s surface, even if very few electrons were accelerated onto the film’s active layer. Importantly, the active layer’s ability to absorb radiation doses can affect the delivered radiation dose. When SEM images are obtained through electrons accelerated at low voltages, the image noise increases, potentially affecting measurement accuracy. We acquired our SEM images using an optimized level of 10 kV, exposing the film to as few electron rays as possible. Consequently, our maximum exposure time was 10 seconds or less.

We investigated the feasibility of measuring EBT3 film microscopically. We visually determined the effects of radiation by observing changes to the active layer’s molecular structure following irradiation. These changes were quantified using texture analysis and were highly correlated with the delivered dose. These results confirm that irradiated film radiation levels can be accurately determined using a radiation dose calibration curve.

We confirmed a high correlation between EBT3 film surface texture and delivered radiation doses. Our methods allowed us to analyze microscopic changes the film’s active layer that can subsequently be used for dosimetry.

This study was supported by a VHS Medical Center Research Grant, Republic of Korea (grant number: VHSMC 22016).

The data that support the findings of this study are available on request from the corresponding author.

  1. Casanova Borca V, Pasquino M, Russo G, Grosso P, Cante D, Sciacero P, et al. Dosimetric characterization and use of GAFCHROMIC EBT3 film for IMRT dose verification. J Appl Clin Med Phys. 2013;14:4111.
    Pubmed KoreaMed CrossRef
  2. Zeidan OA, Stephenson SA, Meeks SL, Wagner TH, Willoughby TR, Kupelian PA, et al. Characterization and use of EBT radiochromic film for IMRT dose verification. Med Phys. 2006;33:4064-4072.
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  3. Marrazzo L, Zani M, Pallotta S, Arilli C, Casati M, Compagnucci A, et al. GafChromic® EBT3 films for patient specific IMRT QA using a multichannel approach. Phys Med. 2015;31:1035-1042.
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  4. Ocadiz A, Livingstone J, Donzelli M, Bartzsch S, Nemoz C, Kefs S, et al. Film dosimetry studies for patient specific quality assurance in microbeam radiation therapy. Phys Med. 2019;65:227-237.
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  5. Stella G, Cavalli N, Bonanno E, Zirone L, Borzì GR, Pace M, et al. SBRT/SRS patient-specific QA using GAFchromicTM EBT3 and FilmQATM Pro software. J Radiosurg SBRT. 2022;8:37-45.
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  6. Liu HW, Gräfe J, Khan R, Olivotto I, Barajas JE. Role of in vivo dosimetry with radiochromic films for dose verification during cutaneous radiation therapy. Radiat Oncol. 2015;10:12.
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  7. Moylan R, Aland T, Kairn T. Dosimetric accuracy of Gafchromic EBT2 and EBT3 film for in vivo dosimetry. Australas Phys Eng Sci Med. 2013;36:331-337.
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  8. Hartmann B, Martisiková M, Jäkel O. Homogeneity of Gafchromic EBT2 film. Med Phys. 2010;37:1753-1756.
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  9. Mizuno H, Takahashi Y, Tanaka A, Hirayama T, Yamaguchi T, Katou H, et al. Homogeneity of GAFCHROMIC EBT2 film among different lot numbers. J Appl Clin Med Phys. 2012;13:3763.
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  10. Martisíková M, Ackermann B, Jäkel O. Analysis of uncertainties in Gafchromic EBT film dosimetry of photon beams. Phys Med Biol. 2008;53:7013-7027.
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  11. Saur S, Frengen J. GafChromic EBT film dosimetry with flatbed CCD scanner: a novel background correction method and full dose uncertainty analysis. Med Phys. 2008;35:3094-3101.
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  12. Marroquin EY, Herrera González JA, Camacho López MA, Barajas JE, García-Garduño OA. Evaluation of the uncertainty in an EBT3 film dosimetry system utilizing net optical density. J Appl Clin Med Phys. 2016;17:466-481.
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  13. Palmer AL, Bradley D, Nisbet A. Evaluation and implementation of triple-channel radiochromic film dosimetry in brachytherapy. J Appl Clin Med Phys. 2014;15:4854.
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  14. Holm KM, Yukihara EG, Ahmed MF, Greilich S, Jäkel O. Triple channel analysis of Gafchromic EBT3 irradiated with clinical carbon-ion beams. Phys Med. 2021;87:123-130.
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  15. Ghalati MK, Nunes A, Ferreira H, Serranho P, Bernardes R. Texture analysis and its applications in biomedical imaging: a survey. IEEE Rev Biomed Eng. 2022;15:222-246.
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  16. Colen RR, Rolfo C, Ak M, Ayoub M, Ahmed S, Elshafeey N, et al. Radiomics analysis for predicting pembrolizumab response in patients with advanced rare cancers. J Immunother Cancer. 2021;9:e001752.
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  17. Brynolfsson P, Nilsson D, Torheim T, Asklund T, Karlsson CT, Trygg J, et al. Haralick texture features from apparent diffusion coefficient (ADC) MRI images depend on imaging and pre-processing parameters. Sci Rep. 2017;7:4041.
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  18. Rui W, Qiao N, Wu Y, Zhang Y, Aili A, Zhang Z, et al. Radiomics analysis allows for precise prediction of silent corticotroph adenoma among non-functioning pituitary adenomas. Eur Radiol. 2022;32:1570-1578.
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Article

Original Article

Progress in Medical Physics 2022; 33(4): 158-163

Published online December 31, 2022 https://doi.org/10.14316/pmp.2022.33.4.158

Copyright © Korean Society of Medical Physics.

Determination of Absorbed Dose for Gafchromic EBT3 Film Using Texture Analysis of Scanning Electron Microscopy Images: A Feasibility Study

So-Yeon Park

Department of Radiation Oncology, Veterans Health Service Medical Center, Seoul, Korea

Correspondence to:So-Yeon Park
(vsoyounv@gmail.com)
Tel: 82-2-2225-4648
Fax:82-2-2225-4640

Received: November 28, 2022; Revised: December 19, 2022; Accepted: December 20, 2022

This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose: We subjected scanning electron microscopic (SEM) images of the active layer of EBT3 film to texture analysis to determine the dose-response curve.
Methods: Uncoated Gafchromic EBT3 films were prepared for direct surface SEM scanning. Absorbed doses of 0–20 Gy were delivered to the film’s surface using a 6 MV TrueBeam STx photon beam. The film’s surface was scanned using a SEM under 100× and 3,000× magnification. Four textural features (Homogeneity, Correlation, Contrast, and Energy) were calculated based on the gray level co-occurrence matrix (GLCM) using the SEM images corresponding to each dose. We used R-square to evaluate the linear relationship between delivered doses and textural features of the film’s surface.
Results: C orrelation r esulted i n h igher l inearity a nd d ose-response c urve s ensitivity t han Homogeneity, Contrast, or Energy. The R-square value was 0.964 for correlation using 3,000× magnified SEM images with 9-pixel offsets. Dose verification was used to determine the difference between the prescribed and measured doses for 0, 5, 10, 15, and 20 Gy as 0.09, 1.96, −2.29, 0.17, and 0.08 Gy, respectively.
Conclusions: Texture analysis can be used to accurately convert microscopic structural changes to the EBT3 film’s surface into absorbed doses. Our proposed method is feasible and may improve the accuracy of film dosimetry used to protect patients from excess radiation exposure.

Keywords: Film dosimetry, Gafchromic film, Texture analysis, Scanning electron microscopy

Introduction

Radiochromic film was first developed in 2004 and is the most commonly used dosimetric radiotherapy tool [1]. Gafchromic EBT3 films (Ashland Inc., Wayne, NJ, USA), currently the most widely used radiochromic films, feature high spatial resolution, tissue equivalence characteristics, and the advantage of two-dimensional (2D) measurements [2,3]. These films are also used for quality assurance and to determine in vivo dosimetry when administering advanced radiotherapy techniques like intensity-modulated radiation therapy and volumetric-modulated arc therapy [3-7].

Radiation doses to the EBT3 film surface are determined by obtaining scanner images of the film’s opacity before and after radiation exposure. Radiation dose values are then derived from red-green-blue (RGB) image values which mathematically represents color information using three or four different color parameters. This step is followed by color quantification standardization. However, procedural variables like active layer non-uniformities, scanning non-uniformities, and film scan angle can affect dosimetric accuracy [1,8-11].

Various institutions have evaluated the overall dosimetry uncertainty of EBT3 films according to RGB configurations within various measurement and scanning environments. These experiments revealed the dosimetric uncertainty estimates of 3.2% for R, 4.9% for G, and 5.2% for B channels [12]. Another study proposed a calibration curve that used the triple-channel analysis method to reduce dosimetric uncertainty and relative standard deviation and improve dosimetric accuracy [13,14]. These efforts underscore the importance of accurately measuring radiation doses to EBT3 film; relevant research is ongoing.

Texture analysis quantifies pixels within 2D images that cannot be recognized with the naked eye [15-17]. Texture analysis is used for radiomic analysis of medical images. For example, a patient’s prognosis can be determined using texture analysis. 2D images can be quantified through texture analysis and used for dose measurement [18]. Shih et al. obtained polymer gel surface images using scanning electron microscopy (SEM) after application of various (5, 10, 15, and 20 Gy) radiation doses. The researchers analyzed four textural features to determine potential correlations with the delivered doses [19]. Using the dose calibration curve, the authors found differences in delivered doses of −7.60% for 5 Gy, 5.80% for 10 Gy, 2.53% for 15 Gy, and −0.95% for 20 Gy [19].

Images of the film’s active layer were obtained using SEM after irradiation with various radiation doses. Each SEM image was subjected to texture analysis to determine its relevant features. We additionally determined the dose calibration curve between the calculated and delivered dose values to evaluate the dose calibration curve’s accuracy.

Materials and Methods

1. Radiochromic EBT3 film

The EBT3 film consists of a 28-μm-thick active layer that reacts to radiation and a 125-μm-thick transparent polyester substrate layer that protects the active layer. The substrate layer is positioned above and below the active layer to reduce damage and interference by external ultraviolet (UV) and normal lights. The active layer in the EBT3 film contains yellow-colored, radiation-sensitive chemicals that become opaque after polymerization from radiation exposure. The adjusted opacity value obtained from each of the RGB channels is used to calculate optical density, which strongly correlates with radiation dose. We purchased EBT3 film samples with the upper substrate layer removed to directly image the active layer’s surface (Fig. 1). Because EBT3 film is sensitive to UV and general light, the samples were stored in a dark room except during irradiation and the acquisition of SEM images.

Figure 1. Depiction of Gafchromic EBT3 film’s surface structure. (a) Laminated EBT3 film. (b) Unlaminated EBT3 film.

2. Irradiation

All EBT3 film samples were cut into 1×1 cm2 pieces and placed on a 5-cm thick solid water phantom and covered with oil paper to prepare for irradiation and prevent scratching of the active layer’s surface. A 1.5-cm thick solid water phantom was placed on the EBT3 film’s surface. A 100-cm source-to-surface distance and 10×10 cm2 irradiation field were established. After dose calidation for 6 MV photon rays was performed according to the American Association of Physicians in Medicine’s Task Group 51 protocol, the samples were irradiated using 6 MV photon rays produced by the TrueBeam STx (Varian Medical Systems, Palo Alto, CA, USA) [20] to ensure accurate dose delivery. Radiation doses of 0, 5, 10, 15, and 20 Gy were administered over five sets, using one set of four films. The irradiated films were placed in a dark room for more than 24 hours for self-development.

3. SEM scanning

To obtain the SEM images, we coated the 4-nm-thick EBT3 surfaces with iridium to amplify the electron signals. SEM SNE-4500M (SEC, Suwon, Korea) was for SEM image acquisition in environments of 10 kV and 100 μA. Four measurement points were designated uniformly on each film sample and each measurement point was examined under 100× and 3,000× magnification.

4. Calculation of textural parameters

Texture analysis used a gray level co-occurrence matrix (GLCM) to determine between-pixel relationships. When determining GLCM, the between-pixel distance “d” was changed from 1 to 30, and we used between-pixel angles “θ” of 0°, 45°, 90°, and 135°. The quantization level (Ng) was 64, the level most frequently used for texture analysis. Using GLCM, the four most representative textural features—Entropy, Contrast, Energy, and Homogeneity—were calculated according to the following equations:

Entropy= i=1 Ngj=1Ngp i, jlog(p i,j), 
Contrast= i=1 Ngj=1Ng ij2p i, j,
Energy= i=1 Ngj=1Ngp i, j2 ,
Homogeneity= i=1 Ngj=1Ng1 1+ ij2 p i, j,

here, i and j refer to the horizontal and vertical axis coordinates of GLCM, respectively. The spatial dependence matrix of GLCM is denoted by p(i, j), indicating the probability of a between-pixel relationship for each (i, j).

Four textural features were obtained to determine the distances and angles between pixels. The average between-pixel angle was chosen as the representative value. In other words, for each surface image, we obtained representative values for each of the four textural analysis parameters.

5. Determination of dose calibration curves and statistical analysis

We performed a linear regression analysis to determine the correlation between the textural features and delivered doses and calculated maximum R-squared values to evaluate the correlations between doses and each textural parameter.

Results

Fig. 2 depicts a surface EBT3 film image obtained using SEM. The images that were magnified 3,000× represented the active layer’s structural molecules more clearly than those magnified 100×. As the delivered dose increased, the active layer’s surface became smoother through molecular polymerization.

Figure 2. An EBT3 film surface image obtained using scanning electron microscopic (SEM). Each measurement point is visualized under 100× and 3,000× magnification and absolute radiation doses of 0, 5, 10, 15, and 20 Gy.

Fig. 3 depicts the correlation between textural features and radiation doses as a function of pixel distance. Under 100× magnification, Contrast and Homogeneity had R-squared values of ≥0.5 for all between-pixel distances. For Homogeneity (d=1), the maximum R-squared value was 0.761. Using 3,000× magnification, the R-squared value was ≥0.5 for all between-pixel distances except for the correlation with a d=1–4. Correlation (d=9) produced an R-squared value of 0.964.

Figure 3. The maximum coefficient of determination value based on the between-pixel distance and the textural features obtained following irradiation and under (a) 100× and (b) 3,000× surface magnification.

Fig. 4 depicts the dose calibration curve obtained using correlation (d=9) under 3,000× magnification and with the highest maximum coefficient of determination value. When the radiation dose was calculated based on the dose correction curve of the correlation (d=9), the differences between the actual delivered radiation dose values and calculated dose values were 0.09, 1.96, −2.29, 0.17, and 0.08 Gy for 0, 5, 10, 15, and 20 Gy, respectively.

Figure 4. Correlation curve of the parameter of Correlation (d=9) for the EBT3 film’s surface under 3,000× magnification and various radiation doses.

Discussion

We performed dosimetry on EBT3 film samples using SEM and texture analysis of the samples’ surfaces. SEM was used to visualize the microscopic molecular structure of the film’s active layer. Texture analysis was used to quantify changes in molecular structure caused by radiation. Changes to the film’s surface texture were highly correlated with delivered radiation doses.

Shin et al. [19] reported gradual surface smoothing with delivery of increasingly high radiation doses. These results are consistent with our findings. Arjomandy et al. [21] found that delivering 2–10 Gy doses to EBT2 film surfaces reduced surface roughness at higher doses. Microscopically, the reaction between the radiation particles and the active layer’s chemical molecules elicits polymerization. Volotskova et al. found changes to molecular structure after EBT3 and EBT-XD films were irradiated and then analyzed using SEM surface imaging [22]. The authors found no reduction in surface roughness, unlike our results. Polymerization caused the active surface layer’s needle-shaped structure to elongate as a result of radiation exposure [22].

Because we only used SEM to analyze the EBT3 surface images, surface impurities or defects could have affected our results. However, we avoided using film samples with impurities or defects at the measurement points when we acquired our SEM images. Additionally, SEM uses high-voltage, accelerated electrons that might deliver excess radiation to an object’s surface, even if very few electrons were accelerated onto the film’s active layer. Importantly, the active layer’s ability to absorb radiation doses can affect the delivered radiation dose. When SEM images are obtained through electrons accelerated at low voltages, the image noise increases, potentially affecting measurement accuracy. We acquired our SEM images using an optimized level of 10 kV, exposing the film to as few electron rays as possible. Consequently, our maximum exposure time was 10 seconds or less.

We investigated the feasibility of measuring EBT3 film microscopically. We visually determined the effects of radiation by observing changes to the active layer’s molecular structure following irradiation. These changes were quantified using texture analysis and were highly correlated with the delivered dose. These results confirm that irradiated film radiation levels can be accurately determined using a radiation dose calibration curve.

Conclusions

We confirmed a high correlation between EBT3 film surface texture and delivered radiation doses. Our methods allowed us to analyze microscopic changes the film’s active layer that can subsequently be used for dosimetry.

Acknowledgments

This study was supported by a VHS Medical Center Research Grant, Republic of Korea (grant number: VHSMC 22016).

Conflicts of Interest

The author has nothing to disclose.

Availability of Data and Materials

The data that support the findings of this study are available on request from the corresponding author.

Fig 1.

Figure 1.Depiction of Gafchromic EBT3 film’s surface structure. (a) Laminated EBT3 film. (b) Unlaminated EBT3 film.
Progress in Medical Physics 2022; 33: 158-163https://doi.org/10.14316/pmp.2022.33.4.158

Fig 2.

Figure 2.An EBT3 film surface image obtained using scanning electron microscopic (SEM). Each measurement point is visualized under 100× and 3,000× magnification and absolute radiation doses of 0, 5, 10, 15, and 20 Gy.
Progress in Medical Physics 2022; 33: 158-163https://doi.org/10.14316/pmp.2022.33.4.158

Fig 3.

Figure 3.The maximum coefficient of determination value based on the between-pixel distance and the textural features obtained following irradiation and under (a) 100× and (b) 3,000× surface magnification.
Progress in Medical Physics 2022; 33: 158-163https://doi.org/10.14316/pmp.2022.33.4.158

Fig 4.

Figure 4.Correlation curve of the parameter of Correlation (d=9) for the EBT3 film’s surface under 3,000× magnification and various radiation doses.
Progress in Medical Physics 2022; 33: 158-163https://doi.org/10.14316/pmp.2022.33.4.158

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Korean Society of Medical Physics

Vol.33 No.4
December, 2022

pISSN 2508-4445
eISSN 2508-4453
Formerly ISSN 1226-5829

Frequency: Quarterly

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