Monte Carlo investigation of electron beam output factors versus size of square cutout

Zhang, Geoffrey; Rogers, D. W. O.; Cygler, Joanna; Mackie, Thomas Rockwell

doi:10.1118/1.598582

Cited by 58 publications

(31 citation statements)

References 11 publications

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“…Using the voxel sizes mentioned above, dose/particle values as a function of depth were obtained along the central axis of the beam in phantom. Dose per incident particle

({DP}_{max})

R_{100}

is used as the beam output instead of dose per monitor unit (10) . We chose this approach so that simulations with different numbers of histories could be compared directly.…”

Section: Methodsmentioning

confidence: 99%

Monte Carlo calculations of output factors for clinically shaped electron fields

Turian

Smith

Bernard

et al. 2004

J Applied Clin Med Phys

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We report on the use of the EGS4/BEAM Monte Carlo technique to predict the output factors for clinically relevant, irregularly shaped inserts as they intercept a linear accelerator's electron beams. The output factor for a particular combination—energy, cone, insert, and source‐to‐surface distance (SSD)—is defined in accordance with AAPM TG‐25 as the product of cone correction factor and insert correction factor, evaluated at the depth of maximum dose. Since cone correction factors are easily obtained, we focus our investigation on the insert correction factors (ICFs). An analysis of the inserts used in routine clinical practice resulted in the identification of a set of seven “idealized” shapes characterized by specific parameters. The ICFs for these shapes were calculated using a Monte Carlo method (EGS4/BEAM) and measured for a subset of them using an ion chamber and well‐established measurement methods. Analytical models were developed to predict the Monte Carlo–calculated ICF values for various electron energies, cone sizes, shapes, and SSDs. The goodness‐of‐fit between predicted and Monte Carlo–calculated ICF values was tested using the Kolmogorov–Smirnoff statistical test. Results show that Monte Carlo–calculated ICFs match the measured values within 2.0% for most of the shapes considered, except for few highly elongated fields, where deviations up to 4.0% were recorded. Predicted values based on analytical modeling agree with measured ICF values within 2% to 3% for all configurations. We conclude that the predicted ICF values based on modeling of Monte Carlo–calculated values could be introduced in clinical use.PACS numbers: 87.53.Wz, 87.53.Hv

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“…Using the voxel sizes mentioned above, dose/particle values as a function of depth were obtained along the central axis of the beam in phantom. Dose per incident particle

({DP}_{max})

R_{100}

is used as the beam output instead of dose per monitor unit (10) . We chose this approach so that simulations with different numbers of histories could be compared directly.…”

Section: Methodsmentioning

confidence: 99%

Monte Carlo calculations of output factors for clinically shaped electron fields

Turian

Smith

Bernard

et al. 2004

J Applied Clin Med Phys

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“…It was designed by use of the EGSnrc Monte Carlo code by simulation of electron transport through a Varian Clinac 2100C treatment head and calculation of the dose distributions in a water phantom. The performance of the EGSnrc code in accelerator simulations and dose calculations in a medium have been investigated and confirmed to be very accurate [11][12][13][14][15][16][17]. Unlike other eMLC designs [2][3][4][5] where the field size of the applicator used, and hence that of the jaws, remained unchanged for different field sizes of the eMLC, the complete replacement of the applicator by the dual eMLC will allow for variation in the jaw setting for different eMLC field settings.…”

Section: Introductionmentioning

confidence: 99%

Monte Carlo simulations of electron beams collimated with a dual electron multileaf collimator: a feasibility study

Inyang

Chamberlain

2009

Radiol Phys Technol

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Electron applicators and cut-outs have been used for some time in the delivery of electron beam therapy. A dual electron multileaf collimator (eMLC) consisting of upper and lower eMLCs was designed, and dose distributions of electron beams delivered by it were evaluated by Monte Carlo simulations by use of the EGSnrc Monte Carlo code. The percentage depth dose (PDD), dose profiles, dose gradient falloff (G), depth of maximum dose (R(100)), surface dose, bremsstrahlung background, beam flatness, and penumbra of the dual eMLC were evaluated and compared with those simulated and measured with the standard applicators inserted into the treatment head of the medical linear accelerator (linac). The results showed good agreement in most cases. Specifically, the flatness and penumbra obtained with the dual eMLC were better than those obtained with standard applicators. It is therefore possible to use the proposed dual eMLC in the delivery of electron beam therapy without the need for applicators and cut-outs. This will minimize the inconvenience of placing cut-outs on the patients; also, changes in the required field can be effected without the therapist going into the accelerator room when the dual eMLC is finally automated. The absence of a helium bag between the upper and lower eMLCs did not offer significant changes in the dosimetry parameters compared to the eMLC fitted with the helium bag.

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“…The discrepancies were mostly attributed to the loss of side-scatter electron equilibrium with the decrease in the field size and the increase in electron energy. 29 To further validate the dosimetric verification method developed in this study, an additional set of output measurements was performed at two extended SSDs of 105 and 110 cm for all five available energies (6,9,12,16, and 20 MeV) with a cone size of 15 × 15 cm 2 . The results were compared with the measurements done with a Farmer-type ionization chamber.…”

Section: C1 Output Factorsmentioning

confidence: 99%

Development of an accurate EPID‐based output measurement and dosimetric verification tool for electron beam therapy

Ding

Han

2015

Medical Physics

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Purpose: To develop an efficient and robust tool for output measurement and absolute dose verification of electron beam therapy by using a high spatial-resolution and high frame-rate amorphous silicon flat panel electronic portal imaging device (EPID). Methods: The dosimetric characteristics of the EPID, including saturation, linearity, and ghosting effect, were first investigated on a Varian Clinac 21EX accelerator. The response kernels of the individual pixels of the EPID to all available electron energies (6,9,12,16, and 20 MeV) were calculated by using Monte Carlo (MC) simulations, which formed the basis to deconvolve an EPID raw images to the incident electron fluence map. The two-dimensional (2D) dose distribution at reference depths in water was obtained by using the constructed fluence map with a MC simulated pencil beam kernel with consideration of the geometric and structural information of the EPID. Output factor measurements were carried out with the EPID at a nominal source-surface distance of 100 cm for 2 × 2, 3 × 3, 6 × 6, 10 × 10, and 15 × 15 cm 2 fields for all available electron energies, and the results were compared with that measured in a solid water phantom using film and a Farmer-type ion chamber. The dose distributions at a reference depth specific to each energy and the flatness and symmetry of the 10 × 10 cm 2 electron beam were also measured using EPID, and the results were compared with ion chamber array and water scan measurements. Finally, three patient cases with various field sizes and irregular cutout shapes were also investigated. Results: EPID-measured dose changed linearly with the monitor units and showed little ghosting effect for dose rate up to 600 MU/min. The flatness and symmetry measured with the EPID were found to be consistent with ion chamber array and water scan measurements. The EPID-measured output factors for standard square fields of 2 × 2, 3 × 3, 6 × 6, 10 × 10, 15 × 15 cm 2 agreed with film and ion chamber measurements. The average discrepancy between EPID and ion chamber/film measurements was 0.81% ± 0.60% (SD) and 1.34% ± 0.75%, respectively. For the three clinical cases, the difference in output between the EPID-and ion chamber array measured values was found to be 1.13% ± 0.11%, 0.54% ± 0.10%, and 0.74% ± 0.11%, respectively. Furthermore, the γ-index analysis showed an excellent agreement between the EPID-and ion chamber array measured dose distributions: 100% of the pixels passed the criteria of 3%/3 mm. When the γ-index was set to be 2%/2 mm, the pass rate was found to be 99.0% ± 0.07%, 98.2% ± 0.14%, and 100% for the three cases. Conclusions: The EPID dosimetry system developed in this work provides an accurate and reliable tool for routine output measurement and dosimetric verification of electron beam therapy. Coupled with its portability and ease of use, the proposed system promises to replace the current film-based approach for fast and reliable assessment of small and irregular electron field dosimetry. C 2015 American Association of Physicists in...

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Monte Carlo investigation of electron beam output factors versus size of square cutout

Cited by 58 publications

References 11 publications

Monte Carlo calculations of output factors for clinically shaped electron fields

Monte Carlo calculations of output factors for clinically shaped electron fields

Monte Carlo simulations of electron beams collimated with a dual electron multileaf collimator: a feasibility study

Development of an accurate EPID‐based output measurement and dosimetric verification tool for electron beam therapy

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