Net Optical Density Research Articles

Evaluation of a Commercially Available Radiochromic Film for Use as a Complementary Dosimeter for Rapid In-field Low Photon Equivalent Radiation Dose (≤50 mSv) Monitoring.

This work investigates the low photon radiation dose (≤50 mSv) response of commercially available radiochromic films as a potential field dosimeter that could be used by the Canadian Armed Forces to complement their existing personal radiation dosimeters. The films were exposed to various photon energies from x-ray devices and radioisotopes (cesium-137, cobalt-60, and americium-241), and their radiation signal was read using three methods: net optical density, UV/visible spectroscopy, and Fourier transform infrared spectroscopy. A complimentary film dosimeter for field usage should, for military use, display a visual color change and detect doses ≤50 mSv. Given the film's radiochromic properties, it was determined that the net optical density method was the most optimal read-out method, which ascertained a minimum detection dose limit of 4.5 mSv under exposure to a clinical orthovoltage operated at 100 kVp. The film presented an overall linear relationship between net optical density and radiation dose; however, they also portrayed a photon energy-dependent response between 0-100 mSv. Overall, the radiochromic films presented a real-time visual dose signal that could be interpreted rapidly in a mobile laboratory and possessed the ability to detect photon doses ≤50 mSv below the vendor's recommended limits, making it a suitable option as a complementary, disposable, military dosimetric tool. Future work includes the investigation of the film's response under multi- and unknown source environments and environmental-dependent factors such as UV/sunlight exposure and extreme temperatures.

EBT3 Radiochromic film response in time-dependent thermal environment and water submersion conditions: Its clinical relevance and uncertainty estimation

AimThis study aimed to find the thermal and humidity-dependent behavior of EBT3 film. The changes in the film sensitivity as well as the dosimetric region of interest in the small-size film due to its storage and setup condition were evaluated. Material and methodsThree sets of films were kept at three different thermal storage conditions. 15 films from each set were kept at 2 °C, 20 °C, and 40 °C storage conditions for 24 h and 48 h pre- and post-irradiation. The humidity effect (water submersion) on the film in terms of the film's edge diffusion, and change in the optical density at the central region of the film was estimated by keeping the films underwater. ResultsThe mean relative film sensitivity was found 1.107 ± 0.123 and 0.966 ± 0.028 respectively for the films stored at 40 °C and 2 °C with respect to the sensitivity of the films that were kept at room temperature (20 °C) each for 48 h. The dosimetric result shows that the measured dose in the dose range (2–20 Gy) was overestimated by 7.01 % (percentage mean dose difference (MDD)) in the films stored at 40 °C for 48 h. In contrast, it was underestimated by −4.54 % (MDD) in the films stored at 2 °C for 48 h compared to those kept at an ambient room temperature of 20 °C (MDD = 0.24%). The water-diffusion rate at the border of the EBT3 film used in this study was 0.23 mm/h. An increment of 6.8% in the optical density at the central region of the film was observed for the unexposed control film kept underwater for 24 h. The combined standard uncertainty due to five different sources of uncertainties was 2.91%. ConclusionThe sensitivity of the EBT3 film kept at 40 °C is always higher (overestimate) whereas lower (underestimate) for the films kept at 2 °C as compared to the films at normal room temperature. The correction for the changes in the net optical density due to its storage condition (thermal effect) and the dosimetry condition of water submersion (humidity effect) must be incorporated into the current protocols of film-dosimetry if the facility cannot have temperature-controlled film storage environment and if the film immersion under water is more than 4 h.

Systematic characterization of new EBT4 radiochromic films in clinical x-ray beams

Objective. We aim to characterize kinetics of radiation-induced optical density in newly released EBT4 radiochromic films exposed to clinical x-rays. Several film models and batches were evaluated for the film sensitivity, optical signal increasing with time, relative film noise, and minimum detectable limits (MDL).Approach. Radiochromic film pieces from a single batch of EBT3 and three batches of EBT4 were exposed to doses of 77.38 cGy, 386.92 cGy, and 773.84 cGy using a 6 MV x-ray beam. The films were scanned with a flatbed scanner at specific time intervals up to 120 h. The time-series net optical density of red, green and blue colors was corrected for response of the scanner with time and studied to establish the saturation characteristics of film polymerization process. Dose-response from 3.86 cGy to 1935 cGy was also determined for each color. MDL of the films was quantitatively defined as the dose that would double the net optical density of red color above the standard deviation of the residual signal at zero dose. The relative noise characteristics of EBT3 versus EBT4 were studied as a function of time, dose and scanner resolution.Main Results. For doses ≥ 100 cGy, analysis revealed a stability of optical density beyond 48 h post-exposure for EBT3 and EBT4 films. EBT3 films attained 80%-90% of their net optical density at 48 h within minutes of irradiation, compared to 72%-88% for EBT4 films. The rate of growth was slowest for blue color, fastest for red, while green was in between the two. The MDL for EBT4 averaged 15 cGy for three batches, whereas EBT3 films reliably detected doses as low as 8.5 cGy.Significance. Several batches of the new EBT4 film showed slightly lower response compared to its predecessor over 3.86 cGy to 1935 Gy range. For all practical purposes, the post-irradiation growth of polymers ceases between 48 to 60 h for both EBT films. Overall, the EBT4 film exhibited noise characteristics similar to EBT3, except for lower doses where the noise was observed to be higher than its predecessor.

Characterization of a new low-dose and low-energy Gafchromic film LD-V1.

To characterize the dose-response, energy dependence, postexposure changes, orientation dependence, and spatial capabilities of LD-V1, a new low-dose Gafchromic film for low-energy x-ray dosimetry. A single sheet of LD-V1 Gafchromic film was cut into 15 × 20mm2 rectangles with a notch to track orientation. Eight different doses between 5 and 320mGy were delivered by an MXR-160/22 x-ray tube using x-ray beams of 90, 100, and 120kVp filtered with 3mm of Al and 2mm of Ti. The 120kVp films were scanned at 1, 1.5, 2, 3, 12, 24, 48, 72, and 168h postexposure in portrait orientation and additionally scanned in landscape orientation at 24h. The 90 and 100kVp films were scanned at 24h postexposure in portrait orientation. Lastly, a 20 × 200mm2 strip of film was irradiated using a thin-slit imaging collimator and scanned 24h postexposure to test the film performance in an x-ray imaging application. Of the three color channels, the red channel was found to produce a dose-response curve with a large range of net optical density (netOD) values across the considered dose range. A prominent energy dependence was discovered, resulting in dose discrepancies on the scale of 17mGy between 90 and 120kVp for a dose of 80mGy. The measured postexposure changes suggest that the calibration irradiation-to-scan time should be longer than 12h with a±4h scanning time window for dose errors of<0.5%. An average dose difference of 3.4% was found between the two scanning orientations. Lastly, noise of 4% was measured in the thin slit collimator film for a dose of 30mGy. We have characterized the LD-V1 film for low-energy, low-dose x-ray dosimetry. Energy, scan-time, and orientation dependencies should be considered when using this film.

Response characterization of radiochromic OC-1 films in photon, electron, and proton beams.

Radiochromic film (RCF) dosimeters with their high spatial resolution and tissue equivalent properties are conveniently used for two-dimensional and small-field dosimetry. OC-1 is a new model of RCF dosimeter that was commercially introduced recently. Due to its novelty there is a need to characterize its response in various radiation beam types. To study the response of OC-1 RCFs to megavoltage clinical x-ray, electron, and proton beams, as well as kilovoltage x-ray beams used in a small animal research irradiator. OC-1 RCFs were cut into ∼4×4 cm2 pieces. RCF samples were irradiated at various dose levels in the range 0.5-120Gy using different modalities; a small animal radiation research platform (SARRP) (220 kVp), a medical linear accelerator (6 MV, 10 MV, 15 MV, 6 MV FFF, 10 MV FFF photon beams, as well as 6 and 20 MeV electron beams), and a gantry-mounted proton therapy synchrocyclotron. In order to study any dependency on the fractionation scheme, same dose was delivered at several fractions to a set of films. Different dose rates in the range 200-600 MU/min were delivered to a set of films to investigate any dose rate dependency. The films were scanned pre-irradiation and at 48h post-irradiation using a flatbed scanner. The net optical density (OD) was measured for red, green, and blue color channel for each film. The orientation dependency was studied by scanning the films at eight different orientations. In order to study the temporal evolution of the response of the films, film samples were irradiated at 10 and 50Gy using 6 MV photon beams and were scanned upon irradiation at certain time intervals up to 3 months. The spectral response of the films were studied over the visible range using a spectrometer. For megavoltage photon, electron, and plateau region of the proton beams, we did not observe a significant dependency on the beam quality, dose rate, and fractionation scheme. At the kV beam, an unusual over-response was observed in the films' net OD. An orientation dependency in the response of the films with a sinusoidal trend was observed. The response of the films increased with time following a double or triple exponential trend. The spectral absorption peaks were blue-shifted with dose. OC-1 RCFs were found to be reliable dosimeters with no significant energy dependency in MV range for photon and electron beams including the FFF beams. They over-respond when irradiated bykV x-ray beams compared to MV x-ray beams. Caution must be exercised to maintain the orientation of the films when scanning. Due to the temporal growth in the net OD of the films, same post-irradiation time interval must be used for scanning the calibration and test films.

Gafchromic EBT3 film provides equivalent dosimetric performance to EBT-XD film for stereotactic radiosurgery dosimetry

The accurate assessment of film results is highly dependent on the methodology and techniques used to process film. This study aims to compare the performance of EBT3 and EBT-XD film for SRS dosimetry using two different film processing methods. Experiments were performed in a solid water slab and an anthropomorphic head phantom. For each experiment, the net optical density of the film was calculated using two different methods; taking the background (initial) optical density from 1) an unirradiated film from the same film lot as the irradiated film (stock to stock (S-S) method), and 2) a scan of the same piece of film taken prior to irradiation (film to film (F-F) method). EBT3 and EBT-XD performed similarly across the suite of experiments when using the green channel only or with triple channel RGB dosimetry. The dosimetric performance of EBT-XD was improved across all colour channels by using an F-F method, particularly for the blue channel. In contrast, EBT3 performed similarly well regardless of the net optical density method used. Across 21 SRS treatment plans, the average per-pixel agreement between EBT3 and EBT-XD films, normalised to the 20 Gy prescription dose, was within 2% and 4% for the non-target (2—10 Gy) and target (> 10 Gy) regions, respectively, when using the F-F method. At doses relevant to SRS, EBT3 provides comparable dosimetric performance to EBT-XD. In addition, an S-S dosimetry method is suitable for EBT3 while an F-F method should be adopted if using EBT-XD.

Assessment of stereotactic high-resolution detectors for stereotactic body radiotherapy: comparative analysis between myQA® SRS and Gafchromic EBT-XD films.

The study aimed to evaluate dosimetry systems used for stereotactic body radiotherapy (SBRT), specifically 2D array dosimetry and film dosimetry systems, for exploring their characteristics and clinical suitability. For this, high-resolution myQA SRS detectors and Gafchromic EBT-XD films were employed. Film analysis included net optical density (OD) values depending on energy, dose rate, scanner orientation, scanning side, and post-exposure growth. For myQA SRS, signal values were evaluated in terms of dose rate (400-1400 MU/min) and angular dependence (0-180° at 30° intervals) along with couch angles of 0°, 45°, and 90°. Pre-treatment verification included 32 SBRT patients for whom myQA SRS results were compared with those obtained with Gafchromic EBT-XD films. Analysis revealed less than 1% deviation in net OD for energy and dose rate dependence. Scanner orientation caused 2.5% net OD variation, with minimal differences between film front and back scan orientations (variance < 1.0%). A rapid OD rise occurred within six hours post-exposure, followed by gradual increase. The myQA SRS detector showed -3.7% dose rate dependence (400 MU/min), while the angular dependence at 90° was -26.7%. A correction factor effectively reduced these differences to < 1%. For myQA SRS, gamma passing rates were-93.6% (2%/1mm), while those for EBT-XD films were-92.8%. Improved rates were observed with 3%/1mm: for myQA SRS-97.9%, and for EBT-XD film-98.16%. In contrast, for 2%/2mm with 10% threshold, for myQA SRS-97.7% and for EBT-XD film-98.97% were obtained. It is concluded that both myQA SRS detectors and EBT-XD films are suitable for SBRT pre-treatment verification, ensuring accuracy and reliability. However, myQA SRS detectors are preferred over EBT-XD film due to the fact that they offer real-time measurements and user-friendly features.

Improvement of performance for flexible film dosimeter by incorporating additive agents

Objective. To evaluate the reduction in energy dependence and aging effect of the lithium salt of pentacosa−10,−12-diynoic acid (LiPCDA) films with additives including aluminum oxide (Al2O3), propyl gallate (PG), and disodium ethylenediaminetetracetate (EDTA). Approach. LiPCDA films exhibited energy dependence on kilovoltage (kV) and megavoltage (MV) photon energies and experienced deterioration over time. Evaluations were conducted with added Al2O3 and antioxidants to mitigate these issues, and films were produced with and without Al2O3 to assess energy dependence. The films were irradiated at doses of 0, 3, 6, and 12 cGy at photon energies of 75 kV, 105 kV, 6 MV, 10 MV, and 15 MV. For the energy range of 75 kV to 15 MV, the mean and standard deviation (std) were calculated and compared for the values normalized to the net optical density (netOD) at 6 MV, corresponding to identical dose levels. To evaluate the aging effect, PG and disodium EDTA were incorporated into the films: sample C with 1% PG, sample D with 2% PG, sample E with 0.62% disodium EDTA added to sample D, and sample F with 1.23% disodium EDTA added to sample D. Main results. Films containing Al2O3 demonstrated a maximum 15.8% increase in mean normalized values and a 15.1% reduction in std, reflecting a greater netOD reduction at kV than MV energies, which indicates less energy dependence in these films. When the OD of sample 1–4 depending on the addition of PG and disodium EDTA, was observed for 20 weeks, the transmission mode decreased by 8.7%, 8.3%, 29.3%, and 27.3%, respectively, while the reflection mode was 5.4%, 3.0%, 37.0%, and 34.5%, respectively. Significance. Al2O3 effectively reduced the voltage and MV energy dependence. PG was more effective than disodium EDTA in preventing the deterioration of film performance owing to the aging effect.

Development and a feasibility study using Gafchromic XRQA2 film as a novel passive radon measurement technique

In the present paper, a novel passive-type radon measurement technique based on Gafchromic XRQA2 film was developed. A Gafchromic XRQA2 film was modified by peeling off a polyester layer to enhance the film sensitivity to alpha particles, which were mainly emitted from radon and its progeny, and the response of the modified Gafchromic XRQA2 film to alpha particles was investigated. The results indicated that, with the increase in time-integrated alpha activity, the darkness of the exposed modified Gafchromic film increased, and only a small alpha energy dependence with less than 2% relative difference in the film response was observed. Next, the modified Gafchromic XRQA2 film was deployed with a RADUET container for radon measurement to evaluate application feasibility, and the radon response of the modified Gafchromic XRQA2 film was compared with the traditional one of a RADUET with CR-39 detector. The radon calibration was investigated using the radon exposure chamber. The obtained calibration functions showed that the net optical density of modified Gafchromic XRQA2 film was directly proportional to the accumulated radon concentration over the exposure period. From the calibration, the minimum and maximum detectable radon concentrations for a three-month measurement period were estimated to be about 390 Bq m−3 and 15,000 Bq m−3, respectively. Moreover, this technique enables to minimize the effect of thoron interference by the RADUET container design. These results suggest that this technique can be used for measuring radon, particularly in areas with potentially high radon concentrations, for example, underground mines and caves.

Comprehensive evaluation and new recommendations in the use of Gafchromic EBT3 film.

Gafchromic film's unique properties of tissue-equivalence, dose-rate independence, and high spatial resolution make it an attractive choice for many dosimetric applications. However, complicated calibration processes and film handling limits its routine use. We evaluated the performance of Gafchromic EBT3 film after irradiation under a variety of measurement conditions to identify aspects of film handling and analysis for simplified but robust film dosimetry. The short- (from 5min to 100h) and long-term (months) film response was evaluated for clinically relevant doses of up to 50Gy for accuracy in dose determination and relative dose distributions. The dependence of film response on film-read delay, film batch, scanner type, and beam energy was determined. Scanning the film within a 4-h window and using a standard 24-h calibration curve introduced a maximum error of 2% over a dose range of 1-40Gy, with lower doses showing higher uncertainty in dose determination. Relative dose measurements demonstrated <1mm difference in electron beam parameters such as depth of 50% of the maximum dose value (R50 ), independent of when the film was scanned after irradiation or the type of calibration curve used (batch-specific or time-specific calibration curve) if the same default scanner was used. Analysis of films exposed over a 5-year period showed that using the red channel led to the lowest variation in the measured net optical density values for different film batches, with doses >10Gy having the lowest coefficient of variation (<1.7%). Using scanners of similar design produced netOD values within 3% after exposure to doses of 1-40Gy. This is the first comprehensive evaluation of the temporal and batch dependence of Gafchromic EBT3 film evaluated on consolidated data over 8years. The relative dosimetric measurements were insensitive to the type of calibration applied (batch- or time-specific) and in-depth time-dependent dosimetric signal behaviors can be established for film scanned outside of the recommended 16-24h post-irradiation window. We generated guidelines based on our findings to simplify film handling and analysis and provide tabulated dose- and time-dependent correction factors to achieve this without reducing the accuracy of dose determination.

Physical wedge as a tool for radiochromic film calibration

Reliable calibration is one of the major challenges in using radiochromic films (RCF) for radiation dosimetry. In this study the feasibility of using dose gradients produced by a physical wedge (PW) for RCF calibration was investigated. The aim was to establish an efficient and reproducible method for calibrating RCF using a PW. Film strips were used to capture the wedge dose profile for five different exposures and the acquired scans were processed to generate corresponding net optical density wedge profiles. The proposed method was compared to the benchmark calibration, following the guidelines for precise calibration using uniform dose fields. The results of the benchmark comparison presented in this paper showed that using a single film strip for measuring wedge dose profile is sufficient for estimating a reliable calibration curve within the recorded dose range. Furthermore, the PW calibration can be extrapolated or extended by using multiple gradients for the optimal coverage of the desired calibration dose range. The method outlined in this paper can be readily replicated using the equipment and expertise commonly found in a radiotherapy center. Once the dose profile and central axis attenuation coefficient of the PW are determined, they can serve as a reference for a variety of calibrations using different types and batches of film. This investigation demonstrated that the calibration curves obtained with the presented PW calibration method are within the bounds of the measurement uncertainty evaluated for the conventional uniform dose field calibration method.

Accelerating and improving radiochromic film calibration by utilizing the dose ratio in photon and proton beams.

PurposeRadiochromic films are versatile 2D dosimeters with high‐resolution and near tissue equivalence. To assure high precision and accuracy, a time‐consuming calibration process is required. To improve the time efficiency, a novel calibration method utilizing the ratio of the same dose profile measured at different monitor units (MUs) is introduced and tested in a proton and photon beam.MethodsThe calibration procedure employs the dose ratio of film measurements of the same relative profile for different absolute dose values. Hence, the ratio of the dose is constant at any point of the profile, but the ratio of the net optical densities is not constant. The key idea of the method is to optimize the calibration function until the ratio of the calculated doses is constant. The proposed method was tested in the dose range between 0.25–12 and 1–6 Gy in a proton and photon beam, respectively. A radial symmetric profile and a rectangular profile were created, both having a central plateau region of about 3 cm diameter and a dose falloff of about 1.5 cm at larger distances. The dose falloff region was used as input for the optimization method and the central plateau region served as dose reference points. Only the plateau region of the highest dose entered the optimization as an additional objective. The measured data were randomly split into differently sized training and test sets. The optimization was repeated 1000 times with random start value initialization using the same start values for the standard and the gradient method. Finally, a proton plan with four dose levels was created, which were separated spatially, to test the possibility of a full calibration within a single measurement.ResultsParameter estimation was possible with as low as one dose ratio used for optimization in both the photon and the proton case, yet exhibiting a high sensitivity on the dose level. The root mean squared deviation (RMSD) of the dose was less than 1% when the dose ratio was in the order of 20, whereas the median RMSD of all optimizations was 1.7%. Using four dose levels for optimization resulted in a median RMSD of 1% when randomly selecting the dose levels. Having at least one dose ratio of about 20 included in the optimization considerably improved the RMSD of the calibration function. Using six or eight dose levels reduced the sensitivity on the dose level selection and the median RMSD was 0.8%. A full calibration was possible in a single measurement having four dose levels in one plan but spatially separated.ConclusionsThe number of measurements required to obtain an EBT3 film calibration function could be reduced using the proposed dose ratio method while maintaining the same accuracy as with the standard method.

Experimental dosimetry of EDR2 films in scanning carbon-ion irradiation.

PurposeTo investigate the dose‐sensitometric response of extended dose range (EDR2) films to scanning carbon‐ion beams and to evaluate the applications of the obtained response curves to carbon‐ion dose distributions.MethodsEDR2 films were irradiated by mono‐energetic scanning carbon‐ion beams with different doses to obtain sensitometric curves at different integrated depth doses (DDDs). Six different DDDs were generated by using a proper buildup for each mono‐energetic beam and were used to investigate the energy dependence. The sensitometric curves were obtained by fitting the net optical density (netOD) to dose at different DDDs. The dose difference between the value converted from the netOD and that calculated in the treatment planning system (TPS) was investigated to evaluate the application scope of the sensitometric curve.ResultsDigitizing the EDR2 film with a resolution of 0.36 (72 dpi) provided a good signal‐to‐noise ratio, and the sensitometric curve was linear at all DDDs of clinically relevant incident kinetic energies in the netOD range of 0.02–1.70 for carbon‐ion film dosimetry. The factors used to convert the netOD to absorbed dose were expressed as a linear function of DDDs, with which the depth dose difference between converted and TPS was less than 3% in the proximal area for incident kinetic energies lower than 307.5 MeV/u.ConclusionThe EDR2 film is a feasible tool for scanning carbon‐ion beam profile measurements by directly evaluating the netOD distribution with proper digitizing resolution and netOD range. By applying the conversion factors, the EDR2 film can also be employed to perform the percentage depth dose consistency checking and linear energy transfer comparison of carbon‐ion lower than 307.5 MeV/u.

Expired EBT3 Films' Sensitivity for the Measurement of X-ray and UV Radiation: An Optical Analysis.

The aim of this study is to compare the optical responses of external beam therapy 3 (EBT3) films exposed to X-rays and solar ultraviolet rays (SUV-rays), as a dose control technique in the clinical sector for various radiation types, energies, and absorbed doses up to 4 Gy. In this study, EBT3 films with three different expiry dates were prepared and cut into pieces of size 2 by 2 cm2. The first group was exposed to 90 kVp X-rays, while the second group was exposed to the SUV-rays at noon. The analysis was performed using a visible Jaz spectrometer and an EPSON Perfection V370 Photo scanner to obtain the absorbance, the net reflective optical density (ROD) and the red-green-blue (RGB) values of the samples. The results have shown that spectroscopic measurements of the exposed expired EBT3 films with these radiation sources are able to produce primary peaks and secondary peaks at λ = 641.74 nm and λ = 585.98 nm for X-rays, and at λ = 637.93 nm and λ = 584.45 nm for SUV-rays, respectively. According to these findings, compared to 2021 films that expired shortly before the trial start date; 2018 films responded better to the absorbed dose than 2016 films when exposed to both X-ray and SUV-rays. In terms of energy dependence, the expired EBT3 2018 had the largest net ROD value. Using L*a*b* indices extracted from the RGB data, and despite that EBT3 films have expiry dates according to the manufacturer; all the films exhibited a substantial colour change, indicating that these films are still usable for clinical and research purposes.

Optical Response of Expired EBT3 Film for Absorbed Dose Measurement in X-ray and Electron Beam Range

The purpose of this study was to investigate the optical response of an expired External Beam Therapy (EBT3) film, which expired in 2018, using X-rays and electron beam doses. The film’s optical responses were evaluated for its usability in measuring different radiation sources, energy, and absorbed doses ranging up to 5 Gy. Pieces of the expired EBT3 film were irradiated with 90 kVp, 6 MV X-ray photons, and 6 MeV electron beam. The analysis was performed using the Jaz visible spectrometer and EPSON Perfection V370 Photo scanner to obtain the absorbance and the net relative optical density (ROD) of the film samples respectively. The results showed that spectroscopic measurements of the exposed expired EBT3 films under these radiation sources were able to produce primary secondary peaks at λ = 633.52 nm and λ = 582.3 nm respectively. The best wavelength subsets that presented the best MLR regression fitting for all experiments were 541.48 nm, 561.11 nm, and 600.28 nm. While, for the 6 MV photon and the 6 MeV electron beam they were 600.28 nm, 650.79 nm and 654.10 nm. In case of the irradiation with the 6 MV photon and the 6 MeV electron beam, expired EBT3 film showed no significant differences, which made it suitable for dosimetry in various sources of radiation. The individual calibration of radiation dose produces very high measurement accuracy with coefficient of determination, R2 above 0.99 and root mean square of error, RMSE of 0.038 Gy, 0.113 Gy, and 0.115 Gy for films irradiated with 90 kVp X-rays, 6 MV photon beam, and 6 MeV electron beam respectively. Hence, from the results, the expired EBT3 film used in this study showed promising usability of expired EBT3 films beyond their prescribed expiry dates.

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

AimThe 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 MethodsTen 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.ResultsGamma 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.ConclusionsWe 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.

Response of HD-V2 radiochromic film to argon ions* *Project supported by the National Natural Science Foundation of China (Grant Nos. U1930107 and 11827807) and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grants Nos. XDA25030100, XDA25010000, and XDB16010200).

A two-dimensional dose detector for ion beam is required in many high energy density physics experiments. As a solid detector, the GAFChromic film offers a good spatial resolution and dosimetric accuracy. For an absolute dose measurement, the relative effectiveness, which represents the darkening efficiency of the film to a radiation source, needs to be taken into consideration. In this contribution, the dose-response of HD-V2 to argon ions is presented for the first time. The calibration was taken over the dose range of 65 Gy–660 Gy with 8-keV argon ions. The response of net optical density is from 0.01 to 0.05. Triple-color dose-response functions are derived. The relative effectiveness for the argon ion beams is about 5%, much lower than that of protons and carbon ions. To explain this effect, the inactivation probability based on track theory of ion bombardment is proposed. Furthermore, a theoretical prediction of the relative effectiveness for single ion is presented, showing the dependence of the darkening efficiency on the atomic number and the incident energy of ions.

Measuring fluence distribution of intense short laser based on the radiochromic effect.

This Letter demonstrates a novel, to the best of our knowledge, method to measure the fluence distribution of an intense short laser pulse based on the radiochromic effect. We discovered that an intense short laser pulse can induce the color reaction with a radiochromic film (RCF). Further, the net optical density of an irradiated RCF is proportional to the fluence of the incident laser pulse in a large range (${2 {-} 120}\;{{{\rm mJ}/{\rm cm}}^2}$). This method supports a large detection area up to near square-meter scale by splicing multi-pieces of RCFs (${8} \times 10\;{{\rm inch}^2}$ each). The spatial resolution reaches as high as 60 lines/mm. It offers a thin-film (${\sim}{100}\;{\unicode{x00B5}{\rm m}}$ thick), flexible, vacuum-compatible solution to intense short laser measurements, especially to laser facilities above petawatt, with beam sizes up to near square-meter scale, e.g., extreme light infrastructure.

Computation of epistemic uncertainty due to limited data samples in small field dosimetry using Fuzzy Set Theory.

To estimate the epistemic (or fuzzy) uncertainty, arising due to limited data samples in the measurement of the output factors (OFs) of the small fields using Fuzzy Set Theory (FST). EBT3 film samples of size 50 × 50 mm2 were used for the measurement of the OF of stereotactic radiosurgery (SRS) cones of size 4, 6, 7.5, 10, 12.5 and 15 mm diameter, normalized with respect to the output of 100 × 100 mm2 open field size. Three measurements were done per cone/field size. Red color channel was chosen for the dosimetry purpose, net optical density (NOD) was converted to the dose using non-linear relation. To estimate the epistemic uncertainty associated with the measured OFs due to limited number of data samples, a triangular fuzzy number (TFN) was assumed as the fuzziness in the dose delivered by the individual SRS cone/field. Uncertainty in the OF was estimated by applying the Fuzzy Vertex Method (FVM). The membership functions of the OF were constructed for each cone size and the nature of the uncertainty in the OF of the cones was expressed in the terms of its fuzziness. For the sake of completeness of the study, the statistical uncertainty involved in the procedure has also been calculated. The statistical and fuzzy uncertainties in the measurement of OF of cones range from 3.28 to 6.25% and 2.58 to 5.44% respectively. The smallest cone of 4 mm has the largest values of statistical and fuzzy uncertainties. The membership functions of the OF for the studied cones were triangular in nature. The epistemic uncertainty arising due to limited number of data samples holds a significant fraction of the prescribed dose, and therefore, should not be ignored in the total uncertainty estimation. This study highlights the significance of epistemic component of measurement uncertainty arising out due to the insufficient/limited number of measurements of a quantity.

Calibration of the EBT3 Gafchromic Film Using HNN Deep Learning.

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.