Monte Carlo simulations of EBT3 film dose deposition for percentage depth dose (PDD) curve evaluation

Robinson, Spencer M.; Esplen, Nolan; Wells, Derek; Bazalova‐Carter, Magdalena

doi:10.1002/acm2.13078

Cited by 11 publications

(8 citation statements)

References 35 publications

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“…However, a recent study by Robinson et al advised against using film in this orientation. 45 It also should be understood that the simulated D Med,Q D Det,Q values in this study only correct for the material differences between film and lung, and do not account for other uncertainties involved with film dosimetry. 41,42,46 Measurements in lung phantoms, particularly of small fields, are becoming increasingly important as more departments attempt to commission or validate treatment planning system calculations for stereotactic ablative radiotherapy treatments of small lung lesions.…”

Section: Discussionmentioning

confidence: 97%

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Technical Note: Small field dose correction factors for radiochromic film in lung phantoms

Charles¹,

Crowe

Kairn

2021

Medical Physics

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Purpose: Radiochromic film has been established as a detector that can be used without the need for perturbation correction factors for small field dosimetry in water. However, perturbation factors in low density media such as lung have yet to be published. This study calculated the factors required to account for the perturbation of radiochromic film when used for small field dosimetry in lung equivalent material. Method: Monte Carlo simulations were used to calculate dose to Gafchromic EBT3 film when placed inside a lung phantom. The beam simulated had a nominal energy of 6 MV and the field sizes simulated ranged from 10 × 10 mm 2 to 30 × 30 mm 2 . The lung density simulated was varied between 0.2 and 0.3 g/cm 3 . Each simulation was repeated with the film replaced by lung material (the same as the surrounding medium), and the required correction factors for film dosimetry in lung ( D Med,Q D Det,Q ) were calculated by dividing the dose in lung by the dose in film. Results: For field sizes 30 × 30 mm 2 and larger, no correction factors were required. At a 20 × 20 mm 2 field size, small corrections were required, but were within the approximate accuracy of film dosimetry (~2%). For a 10 × 10 mm 2 field size, significant correction factors need to be applied (0.935 for lung density of 0.20 g/cm 3 to 0.963 for lung density of 0.30 g/cm 3 ). The values lower than one mean that the film is over-responding. At the "upstream" lung-water interface the correction factors were close to unity; while at the downstream interface the corrections required were marginally smaller to those at the center of lung. One centimeter or more away from the interfaces, the correction factor did not vary as a function distance from the interface (in the beam direction). Away from the central axis (perpendicular to the beam direction), the correction factors increased slightly (away from unity) as a function of off-axis distance, before abruptly changing direction at the penumbra, with the film actually under-responding by~10% outside the field edges. Conclusion: Accurate dosimetry of very small fields (15 × 15 mm 2 or smaller) using radiochromic film requires correction factors for the perturbation of the film on the surrounding lung material. This correction factor was as high as 6.5% for a 10 × 10 mm 2 field size and a density of 0.2 g/cm 3 . This will increase if either the density or the field size decrease further. This correction factor does not vary as a function of depth in lung once charged particle equilibrium is established.

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Section: Discussionmentioning

confidence: 97%

“…Placing the film for example parallel to the beam direction may change the values of

\frac{D_{M e d, Q}}{D_{D e t, Q}}

. However, a recent study by Robinson et al advised against using film in this orientation 45 …”

Section: Discussionmentioning

confidence: 99%

Technical Note: Small field dose correction factors for radiochromic film in lung phantoms

Charles¹,

Crowe

Kairn

2021

Medical Physics

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“…Care was taken to minimize air gaps around the film as this is known to cause minor dose errors. 47 EBT3 film was calibrated using a 6 MV photon beam following the recommendations in the AAPM Task group 55 report. 48 Films were scanned using an EPSON Perfection V800 flatbed scanner (Epson, Japan), with a resolution of 72 dpi and 48 bit RGB color depth.…”

Section: Methodsmentioning

confidence: 99%

“…Film was placed at selected depths within the solid water phantom that included 1, 15, 20, and 50 mm, whereas the MO Skin TM and microDiamond were used to obtain high resolution, near‐surface measurements with the use of 50 μm polyimide (kapton tape), added layer by layer above the MO Skin TM , and depths to 180 mm using various solid water phantom thicknesses. Care was taken to minimize air gaps around the film as this is known to cause minor dose errors 47 …”

Section: Methodsmentioning

confidence: 99%

Characterizing magnetically focused contamination electrons by off‐axis irradiation on an inline MRI‐Linac

Patterson¹,

Oborn

Cutajar³

et al. 2022

J Applied Clin Med Phys

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The aim of this study is to investigate off -axis irradiation on the Australian MRI-Linac using experiments and Monte Carlo simulations. Simulations are used to verify experimental measurements and to determine the minimum offset distance required to separate electron contamination from the photon field. Methods: Dosimetric measurements were performed using a microDiamond detector, Gafchromic ® EBT3 film, and MOSkin TM . Three field sizes were investigated including 1.9 × 1.9, 5.8 × 5.8, and 9.7 × 9.6 cm 2 . Each field was offset a maximum distance, approximately 10 cm, from the central magnetic axis (isocenter). Percentage depth doses (PDDs) were collected at a source-tosurface distance (SSD) of 1.8 m for fields collimated centrally and off -axis. PDD measurements were also acquired at isocenter for each off -axis field to measure electron contamination. Monte Carlo simulations were used to verify experimental measurements, determine the minimum field offset distance, and demonstrate the use of a spoiler to absorb electron contamination. Results: Off -axis irradiation separates the majority of electron contamination from an x-ray beam and was found to significantly reduce in-field surface dose. For the 1.9 × 1.9, 5.8 × 5.8, and 9.7 × 9.6 cm 2 field, surface dose was reduced from 120.9% to 24.9%,229.7% to 39.2%,and 355.3% to 47.3%,respectively.Monte Carlo simulations generally were within experimental error to MOSkin TM and microDiamond, and used to determine the minimum offset distance, 2.1 cm, from the field edge to isocenter. A water spoiler 2 cm thick was shown to reduce electron contamination dose to near zero. Conclusions: Experimental and simulation data were acquired for a range of field sizes to investigate off -axis irradiation on an inline MRI-Linac. The skin sparing effect was observed with off -axis irradiation, a feature that cannot be achieved to the same extent with other methods, such as bolusing, for beams at isocenter.

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“…One of the greatest challenges in small animal dosimetry is the high spatial resolution required to measure small fields, especially when employing spatially fractionated microbeams, and this is where radiochromic films are second to none. The most widely used and characterized radiochromic film for kilovoltage dosimetry currently is GAFChromic EBT3 film (Ashland Advanced Materials, Bridgewater, NJ) [44][45][46][47][48][49][50][51][52][53][54][55]. EBT3 film has a nominal 28 μm thick active layer (Li-PCDA with dominant peaks at 633 and 595) [56] sandwiched between 125 μm thick matte layers of polyester-substrate, with an optimal dose range between 0.20 and 10 Gy and ≤ 25 μm measurement resolution [57,58].…”

Section: Radiochromic Filmsmentioning

confidence: 99%

A review of small animal dosimetry techniques: image-guided and spatially fractionated therapy

Johnstone,

Bazalova-Carter

2023

J. Phys.: Conf. Ser.

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Research in small animal radiotherapy is a crucial step in clinical translation of novel radiotherapy techniques, either delivered as stand-alone treatment or in combination with other treatments, such as chemotherapy and immunotherapy. In order to efficiently translate preclinical findings to the clinical setting, preclinical radiotherapy must replicate clinical therapy in terms of mode of delivery as well as dose delivery accuracy as closely as possible. In this review article, we focused on the description of dosimetry tools for radiotherapy of small animals delivered with kilovoltage x-ray beams on image-guided irradiators and in a spatially-fractionated manner by means of microbeam therapy. The specifics of dosimetry of kilovoltage x-ray beam deliveries with small, often sub-millimeter, beams are highlighted, and suitable dosimeters, phantoms, and dose measurement and calculation techniques are reviewed. Future directions for accurate real-time high spatial resolution dosimetry of small animal irradiations are also discussed.

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Monte Carlo simulations of EBT3 film dose deposition for percentage depth dose (PDD) curve evaluation

Cited by 11 publications

References 35 publications

Technical Note: Small field dose correction factors for radiochromic film in lung phantoms

Technical Note: Small field dose correction factors for radiochromic film in lung phantoms

Characterizing magnetically focused contamination electrons by off‐axis irradiation on an inline MRI‐Linac

A review of small animal dosimetry techniques: image-guided and spatially fractionated therapy

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