An experimental extrapolation technique using the Gafchromic EBT3 film for relative output factor measurements in small x-ray fields

Morales, Johnny; Butson, Martin J; Crowe, Scott; Hill, Robin; Trapp, Jamie

doi:10.1118/1.4958679

Cited by 34 publications

(39 citation statements)

References 38 publications

(44 reference statements)

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“…One participant irradiated their films in the water phantom, but all others used Virtual Water™ (Med‐Cal, WI, USA) supplied by ARPANSA. One participant used a new extrapolation technique to obtain their final value 18. We do not believe that the use of Virtual Water™ will significantly affect the film‐measured output factors.…”

Section: Resultsmentioning

confidence: 99%

Survey of 5 mm small‐field output factor measurements in Australia

Oliver¹,

Butler²,

Takau³

et al. 2018

J Applied Clin Med Phys

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The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) held a comparison exercise in April 2016 where participants came to ARPANSA and measured the output factor of a nominal 5 mm cone attached to the ARPANSA Elekta Synergy (Elekta, Crawley, UK) linear accelerator. The goal of the exercise was to compare the consistency and methods used by independent medical physicists in measuring small‐field output factors. ARPANSA provided a three‐dimensional scanning tank for detector setup and positioning, but the participants were required to measure the output factor with their own detectors. No information regarding output factors previously measured was supplied to participants to make each result as independent as possible. Fifteen groups travelled to ARPANSA bringing a wide range of detectors and methods. A total of 30 measurements of the output factor were made. The standard deviation of the measurements (excluding one expected outlier from an uncorrected ionization chamber measurement) was 3.6%. The results provide an insight into the consistency of small‐field dosimetry being performed in Australia and New Zealand at the present time.

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Section: Resultsmentioning

confidence: 99%

Survey of 5 mm small‐field output factor measurements in Australia

Oliver¹,

Butler²,

Takau³

et al. 2018

J Applied Clin Med Phys

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“…Response of detectors in small fields and the determination of detector‐specific output correction factors have been extensively investigated for a range of detectors by several research groups, using one of the following three techniques: (a) empirical approach, where uncorrected signal ratios were determined and compared to the field output factors determined with reference detectors, (b) numerical approach, where

k_{Q_{italicclin}, Q_{italicref}}^{f_{italicclin}, f_{italicref}}

were determined with MC simulations, and (c) semi‐empirical approach which combines both, measurements and numerical/analytical calculations, and where

k_{Q_{italicclin}, Q_{italicref}}^{f_{italicclin}, f_{italicref}}

were the most commonly determined through the comparison of measured uncorrected detector's signal ratios with MC calculated field output factors . There are advantages and disadvantages of each of these approaches .…”

Section: Introductionmentioning

confidence: 99%

A novel method for the determination of field output factors and output correction factors for small static fields for six diodes and a microdiamond detector in megavoltage photon beams

et al. 2018

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Purpose The goal of this work is to provide a large and consistent set of data for detector‐specific output correction factors, kQitalicclin,Qitalicref0.166667emfitalicclin,fref, for small static fields for seven solid‐state detectors and to determine field output factors, ΩQitalicclin,Qitalicreffclin,fref, using EBT3 radiochromic films and W1 plastic scintillator as reference detectors on two different linear accelerators and four megavoltage photon beams. Consistent measurement conditions and recommendations given in the International Code of Practice TRS‐483 for small‐field dosimetry were followed throughout the study. Methods ΩQitalicclin,Qitalicreffclin,fref were determined on two linacs, Elekta Versa HD and Varian TrueBeam, for 6 and 10 MV beams with and without flattening filter and for nine fields ranging from 0.5 × 0.5 cm2 to 10 × 10 cm2. Signal readings obtained with EBT3 radiochromic films and W1 plastic scintillator were fitted by an analytical function. Volume averaging correction factors, determined from two‐dimensional (2D) dose matrices obtained with EBT3 films and fitted to bivariate Gaussian function, were used to correct measured signals. kQitalicclin,Qitalicreffclin,fref were determined empirically for six diodes, IBA SFD, IBA Razor, PTW 60008 P, PTW 60012 E, PTW 60018 SRS, and SN EDGE, and a PTW 60019 microDiamond detector. Results Field output factors and detector‐specific kQitalicclin,Qitalicreffclin,fref are presented in the form of analytical functions as well as in the form of discrete values. It is found that in general, for a given linac, small‐field output factors need to be determined for every combination of beam energy and filtration (WFF or FFF) and field size as the differences between them can be statistically significant (P < 0.05). For different beam energies, the present data for kQitalicclin,Qitalicreffclin,fref are found to differ significantly (P < 0.05) from the corresponding data published in TRS‐483 mostly for the smallest fields (<1.5 cm). For the PTW microDiamond detector, statistically significant differences (P < 0.05) between kQitalicclin,Qitalicreffclin,fref values were found for all investigated beams on an Elekta Versa HD linac for field sizes 0.5 × 0.5 cm2 and 0.8 × 0.8 cm2. Significant differences in kQitalicclin,Qitalicreffclin,fref between beams of a given energy but with and without flattening filters are found for measurements made in small fields (<1.5 cm) at a given linac. Differences in kQitalicclin,Qitalicreffclin,fref are also found when measurements are made at different linacs using the same beam energy filtration combination; for the PTW microDiamond detector, these differences were found to be around 6% and were considered as significant. Conclusions Selection of two reference detectors, EBT3 films and W1 plastic scintillator, and use of an analytical function, is a novel approach for the determination of ΩQitalicclin,Qitalicreffclin,fref for small static fields in megavoltage photon beams. Large set of kQitalicclin,Qitalicreffclin,fref data for s...

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“…Radiochromic films have been widely used in radiation therapy dosimetry and quality assurance (QA), especially to compare planned and measured dose distributions. [1][2][3][4][5][6] Such films have been used for in vivo and small field dosimetry as well as in high-dose gradient regions and other challenging scenarios owing to their high spatial resolution, water equivalency, and ease of use. [7][8][9][10][11][12][13][14][15][16] Radiochromic film response to ionizing radiation is manifested as a change in color, due to increase in the concentration of light absorbing polymers, which is characterized by the optical density (OD) or absorbance (A).…”

Section: Introductionmentioning

confidence: 99%

Spectral analysis of the EBT3 radiochromic films for clinical photon and electron beams

et al. 2019

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Purpose The purpose of this study was to investigate the spectral response of the EBT3 radiochromic films to different beam qualities for radiation therapy dosimetry. Dose, dose rate, and interbatch dependencies on the spectral response of the films were investigated as well. Methods Pieces of EBT3 films placed between layers of solid water phantoms were irradiated with 6 and 15 MV photon beams, 6 and 10 MV‐flattening filter free (FFF) photon beams, and 6 and 20 MeV electron beams at dose levels between 0.4 and 50 Gy. Net absorbance was measured as a function of wavelength from the spectra acquired in the wavelength range of 400–800 nm using a fiber‐coupled spectrometer and broadband light source. Results No significant change was observed in the absorption spectra of the EBT3 film from the same batch irradiated with the same amount of dose using different beam qualities. Also, no spectral change with dose rate was observed. The measured net absorbance per Gy was independent of beam quality in the 1–50 Gy dose range. Slight differences in the spectral shape and absorption band positions were observed in film samples from different batches. The net absorbance spectra showed two absorption bands centered around 634–636 nm (primary) and 583–585 nm (secondary). However, depending on the film batch, for doses above a certain level the primary absorption band appears to “split” into two bands centered around ~624–628 and ~641–645 nm. Conclusions The spectral shape of the EBT3 radiochromic films irradiated with photons (including FFF) and electron beams is beam quality and dose rate independent; however, it varies with dose level, batch, and spectroscopy system used.

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An experimental extrapolation technique using the Gafchromic EBT3 film for relative output factor measurements in small x-ray fields

Cited by 34 publications

References 38 publications

Survey of 5 mm small‐field output factor measurements in Australia

Survey of 5 mm small‐field output factor measurements in Australia

A novel method for the determination of field output factors and output correction factors for small static fields for six diodes and a microdiamond detector in megavoltage photon beams

Spectral analysis of the EBT3 radiochromic films for clinical photon and electron beams

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