Spectral analysis of the EBT3 radiochromic film irradiated with 6 MV X-ray radiation

Response of the modified GAFCHROMIC EBT2 radiochromic film to DC glow discharge plasma

The response of the modified GAFCHROMIC EBT2 radiochromic film to DC Oxygen glow discharge plasma was investigated using a flatbed scanner and an UV-Vis spectrophotometer. The film was modified by removing the polyester overlaminate, adhesive, and topcoat layers with a total thickness of 80 µm, and is now referred to as EBT2-M. The EBT2-M films were exposed to DC Oxygen plasma for different durations: 0, 0.5, 1, 2, 3, 4, 7, and 10 min. The exposed films exhibit coloration homogeneity with an average variation of (1.6 ± 0.3) × 10-4 pixel values/µm, irrespective of the applied exposure time. The pixel values of the red-and-green channels and weighted grayscale images decreased exponentially with different sensitivity amounts to [Formula: see text] 39.67, 49.69, and 42.11 min-1, respectively, as the exposure time increased. The two absorption peaks at 580 ± 4 nm and 632 ± 4 nm in the UV-Vis absorption spectra of the exposed GAFCHROMIC EBT2-M radiochromic films are increasing with increasing exposure time up to 4 min, thereafter saturated for prolonged exposure time. The integrated absorbance in the range from 400 to 700 nm is linearly correlated with the exposure time. The indirect and direct optical energy band gaps and Urbach energy of the modified GAFCHROMIC EBT2 film are weakly correlated with the exposure time. These findings suggest the utilization of the modified GAFCHROMIC EBT2 radiochromic film as a novel and simple technique for plasma diagnostics.

Role of water in the crystal structure of LiPCDA monomer and the radiotherapy dose response of EBT-3 film

Purpose

Radiochromic material used in recent commercial films has been suggested as a candidate for in vivo dosimetry because of its dose sensitivity, real‐time response, and atomic composition. It was observed that its sensitive material, lithium pentacosa‐10,12‐diynoate (LiPCDA), can have two distinct forms, with main absorbance peaks at ∼635 and ∼674 nm. The spectrum of the latter is similar to that of pentacosa‐10,12‐diynoic acid (PCDA) used in the commercial predecessor, obtained through desiccation of the commercial film. Water was suggested to be a part of the crystal structure and thus its presence or absence would affect dosimetric parameters. The objective of this study is to: (a) investigate how desiccated commercial films compared to the native form in terms of macroscopic crystal structure, dose–response, signal linearity, and post‐exposure kinetics; (b) demonstrate proof‐of‐concept that the two versions can be combined into one optical dosimeter and measured simultaneously.

Methods

Commercial radiochromic film, EBT‐3, was desiccated for 10 days at 45°C. Using a 6 MV LINAC beam and standard setup of 100 Source to Axis Distance (SAD), 10 cm × 10 cm field size, and 1.5 cm depth, commercial and desiccated films were irradiated to 50, 100, 200, 500, 1000, 2000, 3000 cGy and the latter to 4000, 5000, and 7000 cGy. A custom phantom equipped with optical fibers for real‐time read‐out was used for all measurements. Absorbance spectra were collected at ∼1 Hz before, during, and after irradiation. Data were collected for ∼1 h after the end of irradiation for 200 cGy experiments. The radiation‐induced change in optical density (∆OD) was calculated with a 10 nm band around the primary absorbance peak. The post‐exposure percent optical density change was calculated and compared to ∆OD at the end of irradiation. Both commercial and desiccated films were also irradiated and measured simultaneously as proof‐of‐concept for using two materials within one optical path. For electron microscopy imaging, active materials from commercial and desiccated films were imaged on a scanning electron microscope at an accelerating voltage of 10 kV.

Results

Scanning electron microscope images showed that desiccated film was similar in topographical structure to the commercial EBT‐3 form. It maintained a non‐linear ∆OD with dose but resulted in ∼1/3 signal compared to the commercial film. Evaluation of post‐exposure response showed significantly lower percent increase in ∆OD for desiccated film initially, with no statistically significant difference at 1 h after the end of irradiation. Combining both films and simultaneously measuring their absorbance illustrated that the two absorbance peaks were identifiable and resolvable to allow for an independent determination of dose from each.

Conclusions

Water is implicated in the crystal structure of the EBT‐3 radiochromic film, with its removal through desiccation affecting both dosimetric and spectroscopic characteristics of the material. The two forms of radiochromic material (with and without water) are spectrally resolvable allowing for independent dose determination from each, opening up possibilities for dose measurements at different locations along a single fiber.

Radiochromic Films for the Two-Dimensional Dose Distribution Assessment

Radiochromic films are mainly used for two-dimensional dose verification in photon, electron, and proton therapy treatments. Moreover, the radiochromic film types available today allow their use in a wide dose range, corresponding to applications from low-medical diagnostics to high-dose beam profile measurements in charged particle medical accelerators. An in-depth knowledge of the characteristics of radiochromic films, of their operating principles, and of the dose reading techniques is of paramount importance to exploit all the features of this interesting and versatile radiation detection system. This short review focuses on these main aspects by considering the most recent works on the subject.

Selection of gamma analysis acceptance criteria in IMRT QA using Gafchromic EBT3 film dosimetry

Background and purpose

This study reported the justification and selection of acceptable γ criteria with respect to low (6 MV) and high (15 MV) photon beams for intensity-modulated radiation therapy quality assurance (IMRT QA) using the Gafchromic external beam therapy 3 (EBT3) film.

Materials and methods

Five-field step-and-shoot IMRT was used to treat 16 brain IMRT patients using the dual-energy DHX-S linear accelerator (Varian Medical System, Palo Alto, CA, USA). Dose comparisons between computed values of the treatment planning system (TPS) and Gafchromic EBT3 film were evaluated based on γ analysis using the Film QA Pro software. The dose distribution was analysed with gamma area histograms (GAHs) generated using different γ criteria (3%/2 mm, 3%/3 mm and 5%/3 mm) for the 6 and 15 MV photon beams, to optimise the best distance-to-agreement (DTA) criteria with respect to the beam energy.

Results

From the comparison between the dose distributions acquired from the TPS and EBT3 film, a DTA criterion of 3%/2 mm showed less dose differences (DDs) with passing rates up to 93% for the 6 MV photon beams, while for the 15 MV a relaxed DTA criterion of 5%/3 mm was consistent with the DD acceptability criteria with a 95% passing rate.

Conclusions

Our results suggested that high-energy photon beams required relaxed DTA criteria for the brain IMRT QA, while low-energy photon beams showed better results even with tight DTA criteria.

EBT3 Films in Low Solar Ultraviolet and X-Ray Dose Measurement: A Comparative Analysis

The purpose of this study is to investigate the potentiality of Gafchromic external beam therapy 3 (EBT3) film to measure low dosage of solar ultraviolet (SUV; 0-10 600 mJ/cm2) and x-ray (0-750 mGy) radiation. In this experiment, 2 groups of EBT3 films were prepared with size 2 cm × 1 cm. The first group of films was exposed by incremental SUV dose in the middle of the day. The other group was irradiated by x-ray at 100 kVp, 100 mA, and 2 S of tube voltage, tube current, and exposure time, respectively. The measured SUV consists of 90% ultraviolet A (UVA) and 10% ultraviolet B. The film discoloration was represented by visible absorbance spectroscopy technique using Jaz spectrometer from Ocean Optics Inc. Simple linear regression produced high accuracy with coefficients of determination, r 2 of 0.9804 and root mean square error (RMSE) of 434.88 mJ/cm2 for the measurement of SUV dose. On the other hand, r 2 of 0.98 and RMSE of 31 mGy was produced for the measurement of x-ray dose. The application of multiple linear regression enhanced the measurement accuracy with R 2 of 99% and 99.7% and RMSE of 327.06 mJ/cm2 and 15.045 mGy for SUV and x-ray dose, respectively. The spectral analysis shows a promising measurement at selected wavelengths for SUV and x-ray dose.

Real-time dosimetry with radiochromic films

Radiochromic film dosimetry has been widely employed in most of the applications of radiation physics for over twenty years. This is due to a number of appealing features of radiochromic films, such as reliability, accuracy, ease of use and cost. However, current radiochromic film reading techniques, based on the use of commercial densitometers and scanners, provide values of dose only after the exposure of the films to radiation. In this work, an innovative methodology for the real-time reading of radiochromic films is proposed for some specific applications. The new methodology is based on opto-electronic instrumentation that makes use of an optical fiber probe for the determination of optical changes of the films induced by radiation and allows measurements of dose with high degree of precision and accuracy. Furthermore, it has been demonstrated that the dynamic range of some kinds of films, such as the EBT3 Gafchromic films (intensively used in medical physics), can be extended by more than one order of magnitude. Owing to the numerous advantages with respect to the commonly used reading techniques, a National Patent was filed in January 2018.

Investigation of EBT3 radiochromic film's response to humidity

PURPOSE

The aim of this work is to investigate the effects of immersing EBT3 radiochromic film in water and to evaluate its contribution to the total uncertainty in dose determination.

MATERIALS AND METHODS

We used 3 cm × 3 cm EBT3 radiochromic films irradiated in the range of 0-70 Gy to study the impact of water immersion on the change in net optical density. These films were placed in a water container for a period of 24 h. The net optical density was measured before (0 h) and after of the immersion in water (1, 3, 6, 12, 18, and 24 h). The absorbance spectrum of the EBT3 radiochromic film was measured at 0 h and 24 h after immersion in water. The uncertainty in dose determination due to the effects of keeping the EBT3 radiochromic film submerged in water at 0, 1, and 24 h were recorded in the red, green, and blue channels.

RESULTS

We observed an increase in the net optical density as an effect on the film due to its immersion in water. The penetration of the water at the edges of the radiochromic film was observed to be a function of time during which the film remained in the water. On the other hand, the penetration of water at the edges of the film was found to be independent of irradiation dose.

CONCLUSIONS

EBT3 radiochromic film is found more resistant to water penetration through the edges than its predecessors. However, there is evidence that suggest that liquid water damage the Nylon cover layer of the film by changing its optical properties. Therefore, it is recommended to build a new calibration curve for radiochromic films for a specific situation involving dose measurements in liquid water.

Spectral calibration of EBT3 and HD-V2 radiochromic film response at high dose using 20 MeV proton beams

Radiochromic film is used extensively in many medical, industrial, and scientific applications. In particular, the film is used in analysis of proton generation and in high intensity laser-plasma experiments where very high dose levels can be obtained. The present study reports calibration of the dose response of Gafchromic EBT3 and HD-V2 radiochromic films up to high exposure densities. A 2D scanning confocal densitometer system is employed to carry out accurate optical density measurements up to optical density 5 on the exposed films at the peak spectral absorption wavelengths. Various wavelengths from 400 to 740 nm are also scanned to extend the practical dose range of such films by measuring the response at wavelengths removed from the peak response wavelengths. Calibration curves for the optical density versus exposure dose are determined and can be used for quantitative evaluation of measured doses based on the measured optical densities. It was found that blue and UV wavelengths allowed the largest dynamic range though at some trade-off with overall accuracy.