Evaluation of the uncertainty in an EBT3 film dosimetry system utilizing net optical density

Marroquin, Elsa Y León; González, José Alfredo Herrera; López, Miguel A Camacho; Barajas, Jose Eduardo Villarreal; García‐Garduño, Olivia Amanda

doi:10.1120/jacmp.v17i5.6262

Cited by 140 publications

(133 citation statements)

References 44 publications

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“…This explains why large variations in Net OD for different beam qualities were observed in this work for the blue channel [see Fig (c)]. It may be worth analyzing in detail the response of the EBT‐XD films for doses above 50 Gy using the blue channel for possible use of this film model in treatments requiring high dose per fraction, such as trigeminal neuralgia, taking advantage of the low sensitivity of the films.…”

Section: Resultsmentioning

confidence: 68%

Response characterization of EBT‐XD radiochromic films in megavoltage photon and electron beams

et al. 2019

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Purpose The purpose of this study was to investigate the beam quality dependence of the EBT‐XD radiochromic films for megavoltage photon and electron beam irradiations by studying their spectral response. Dose, dose rate, and interbatch dependencies were investigated as well. Methods EBT‐XD and EBT3 radiochromic films were cut into 5 cm2 × 5 cm2 pieces, placed between solid water phantoms, and irradiated with 6 and 15 MV photon beams, 6 and 10 MV flattening filter free photon beams, and 6 and 20 MeV electron beams at dose levels between 0.5 and 50 Gy. In order to measure the spectral response, the films were illuminated by a deuterium and tungsten‐halogen lamp and net absorption was measured in 400–800 nm spectral range using a fiber‐coupled optical spectrometer. Film samples were then analyzed using a flatbed scanner in the red, green, and blue channel to obtain the optical density of the films. Results The net absorption spectra of the EBT‐XD and EBT3 films showed two absorption bands centered at 635 and 585 nm, characteristic of the EBT model. However, for a given dose, the EBT‐XD films showed lower net absorbance compared to the EBT3 films. At a given dose level, the net absorption spectra and dose–response curves for EBT‐XD films showed only slight variations across various beam qualities. When a calibration curve obtained from a given beam quality is used to measure dose from films irradiated with other beam qualities, the maximum uncertainty in the calculated dose, in ranges 5–40 and 8–50 Gy for red and green channels, respectively, were ~3.1% and ~2.4%. Conclusions The response of the EBT‐XD films is dose rate independent but batch dependent. No significant beam quality dependence was observed in EBT‐XD films in the dose range up to 50 Gy.

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Section: Resultsmentioning

confidence: 68%

Response characterization of EBT‐XD radiochromic films in megavoltage photon and electron beams

et al. 2019

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“…In addition, the dose–response curve was separately plotted for low dose regions up to 50 cGy because a low lens dose was received each time. These curves were fitted to a power function defined as

n e t O D = a \cdot D + b \cdot D^{n}

where a , b , and n are the fitting parameters and D is the measured dose in Gy . Subsequently, the sensitivity of the CLOD was defined as the derivative of the slope of dose–response curve at each point, given by the following equation:

Sensitivity = \frac{italicdnetOD}{italicdD} = a + n b D^{n - 1}

where a, b, and n are defined in Eq.…”

Section: Methodsmentioning

confidence: 99%

Contact lens‐type ocular in vivo dosimeter for radiotherapy

et al. 2019

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Purpose This study aimed to (a) develop a contact lens‐type ocular in vivo dosimeter (CLOD) that can be worn directly on the eye and (b) assess its dosimetric characteristics and biological stability for radiation therapy. Methods The molder of a soft contact lens was directly used to create the dosimeter, which included a radiation‐sensitive component — an active layer similar to a radiochromic film — to measure the delivered dose. A flatbed scanner with a reflection mode was used to measure the change in optical density due to irradiation. The sensitivity, energy, dose rate, and angular dependence were tested, and the uncertainty in determining the dose was calculated using error propagation analysis. Sequential biological stability tests, specifically, cytotoxicity and ocular irritation tests, were conducted to ensure the safe application of the CLOD to patients. Results The dosimeter demonstrated high sensitivity in the low dose region, and the sensitivity linearly decreased with the dose. The responses obtained for the 10 and 15 MV photon beams were 1.7% and 1.9% higher compared to the 6 MV photon beam. A strong dose rate dependence was not obtained for the CLOD. Angular dependence was observed from 90° to 180° with a difference in response from 1% to 2%. The total uncertainty in error propagation analysis decreased as a function of the dose in the red channel. For a dose range of 0 to 50 cGy, the total uncertainties for 5, 10, and 50 cGy were 14.2%, 8.9%, and 5%, respectively. Quantitative evaluation using the MTT (3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide) method presented no cytotoxicity. Further, no corneal opacity, iris reaction, or conjunctival inflammation was observed. Conclusions The CLOD is the first dosimeter that can be worn close to the eye. The results of cytotoxicity and irritation tests indicate that it is a stable medical device. The evaluation of dose characteristics in open field conditions shows that the CLOD can be applied to an in vivo dosimeter in radiotherapy.

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“…2 film immersed for 0.5 h and scanned 24 h postimmersion was 0.6 cGy 16. All films analyzed will be immersed in water for the minimum amount of time possible and for no longer than 0.5 h. According to Marroquin et al., Gafchromic film is more sensitive in the dose range of 0–6 Gy when scanning with the red channel, whereas from 6 to 35 Gy, the response is more sensitive scanning with the green channel 17. For doses greater than 35 Gy, the sensitivity in the response of the film is maximized if the film is scanned with the blue channel.…”

Section: Methodsmentioning

confidence: 98%

Investigation of a source model for a new electronic brachytherapy tandem by film measurement

Martin

Sowards

Wang

2018

J Applied Clin Med Phys

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PurposeTo investigate the accuracy of a vendor‐supplied source model for a new Xoft Axxent 0‐degree titanium tandem by film measurement.MethodsWe measured the anisotropy factors at varying distances and angles from the tandem in water using radiochromic film (Gafchromic EBT3) and an Epson Perfection v750 desktop flatbed scanner (US Epson, Long Beach, CA). A 0‐degree tandem was placed vertically in a water phantom. Four pieces of film, each at varying depths, were positioned orthogonal to the longitudinal axis of the tandem for azimuthal anisotropy measurements. Polar anisotropy measurements were taken with the film aligned parallel to the tandem. An absolute dose calibration for the film was verified with a PTW 34013 Soft X‐Ray Chamber. The film measurements were analyzed using different color channels. The measured polar anisotropy for varying source positions was compared to the vendor's data. Azimuthal anisotropy was measured as a function of the radius and angle, and normalized to the mean value over all angles at the specified radius.ResultsThe azimuthal anisotropy of the tandem and source was found to be consistent for different positions along the tandem's longitudinal axis and at varying distances from the tandem. Absolute dose using a calibrated parallel plate chamber showed agreement to within 2% of expected TPS values. The custom tandem, which has a thicker tip than the wall, was attenuating the 50 kV photons more than expected, at the angles where the photons had more wall material to traverse. This discrepancy was verified at different distances from the tandem and with different measurement techniques. As distance increased, anisotropy values had better agreement.ConclusionsWe quantified the agreement between the measured and provided anisotropy factors for a new Xoft Axxent 0‐degree titanium tandem. Radiochromic film response at low kV energy was also investigated. Our results showed that vendor‐supplied TG‐43 values were appropriate for clinical use at majority of the angles. A rigorous quality assurance method for new electronic brachytherapy sources and applicators, along with complete knowledge of all dosimetric measuring tools, should be implemented for all parts of the verification and commissioning process.

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Evaluation of the uncertainty in an EBT3 film dosimetry system utilizing net optical density

Cited by 140 publications

References 44 publications

Response characterization of EBT‐XD radiochromic films in megavoltage photon and electron beams

Response characterization of EBT‐XD radiochromic films in megavoltage photon and electron beams

Contact lens‐type ocular in vivo dosimeter for radiotherapy

Investigation of a source model for a new electronic brachytherapy tandem by film measurement

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