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Monte Carlo linear accelerator simulation of megavoltage photon beams: Independent determination of initial beam parameters
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10.1118/1.3668315
/content/aapm/journal/medphys/39/1/10.1118/1.3668315
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/39/1/10.1118/1.3668315

Figures

Image of FIG. 1.
FIG. 1.

Measured (ionization chamber; CC13) and calculated depth doses for optimal electron energies, all normalized at 10 cm depth. (a) The 6 MV beam. (b) The 15 MV beam. The radial intensity of the electron beam (given by the standard deviation of a Gaussian distribution), σ, was 1.0 mm in the BEAMnrc simulations. Field size: 5 × 5 cm2, SSD = 90 cm. The insets show relative deviations between simulations and measurements for various incident electron energies.

Image of FIG. 2.
FIG. 2.

Calculated penumbrae for (a) the 6 MV beam and (b) the 15 MV beam, for different electron radial intensities (field size: 5 × 5 cm2, depth: 10 cm, SSD: 90 cm). The field borders are defined by the jaws in both in-plane and cross-plane directions by using different collimator rotations. Penumbra profiles for σ = 0.0, 0.5, 1.0, and 1.5 mm are shown (calculations based on σ = 0.25, 0.75, and 1.25 mm were also performed, but are omitted for clarity). In (c) and (d), the measured penumbrae in both directions, for the 6 MV beam and the 15 MV beam, respectively, are shown together with the simulations that best fitted the measured data (see Fig. 3).

Image of FIG. 3.
FIG. 3.

Root mean squared difference between simulations and measurements in the penumbra region for different values of the incident electron intensity distribution (sigma). Field size: 5 × 5 cm2, SSD = 90 cm. (a) The 6 MV beam (simulated with 6.45 MeV electrons). (b) The 15 MV beam (simulated with 13.35 MeV electrons).

Image of FIG. 4.
FIG. 4.

Measured and calculated in-plane dose profiles of 40 × 40 cm2 fields with parameters based on the results from Secs. III A and III B (without angular spread of the incident electrons). (a) The 6 MV beam (electron energy = 6.45 MeV; σin-plane = 0.25 mm; σcross-plane = 1.0 mm). (b) The 15 MV beam (electron energy = 13.35 MeV; σin-plane = σcross-plane = 0.5 mm). Similar results were found for the cross-plane direction, and are therefore not shown.

Image of FIG. 5.
FIG. 5.

Measured and calculated cross-field dose profiles for square fields at 1.5 cm depth (6 MV beam), 3 cm depth (15 MV beam), and 10 cm depth (both beams). [(a) and (c)] The 6 MV beam in in-plane and cross-plane directions, respectively. Electron energy = 6.45 MeV; σin-plane = 0.25 mm; σcross-plane = 1.0 mm; mean angular spread = 0.7°. [(b) and (d)] The 15 MV beam in in-plane and cross-plane directions, respectively. Electron energy = 13.35 MeV; σin-plane = σcross-plane = 0.5 mm; mean angular spread = 0.5°. The field sizes are 5 × 5, 10 × 10, 20 × 20, and 40 × 40 cm2. Curves represent ionization chamber measurements, symbols represent Monte Carlo simulations.

Image of FIG. 6.
FIG. 6.

Measured and calculated build-up doses for 5 × 5 cm2 fields. Parameters for the 6 MV beam were: electron energy = 6.45 MeV; σin-plane = 0.25 mm; σcross-plane = 1.0 mm; mean angular spread = 0.7°. Parameters for the 15 MV beam were: electron energy = 13.35 MeV; σin-plane = σcross-plane = 0.5 mm; mean angular spread = 0.5°.

Image of FIG. 7.
FIG. 7.

(a) An MLC-shaped field used for verification of the radial intensity of the incident electron beam. Dose profiles were extracted in the direction perpendicular to the leaf motion, as depicted by the red line. The field was used with 0° and 90° collimator rotation, thus profiles in the in-plane and cross-plane direction were obtained. The doses are normalized to the dose at 1.75 cm off-axis, as depicted by the red cross. (b) Measured and calculated dose profiles for the 6 MV beam. Monte Carlo parameters: electron energy = 6.45 MeV; σin-plane = 0.25 mm; σcross-plane = 1.0 mm; mean angular spread = 0.7°. (c) Measured and calculated dose profiles for the 15 MV beam. Monte Carlo parameters: electron energy = 13.35 MeV; σin-plane = σcross-plane = 0.5 mm; mean angular spread = 0.5°. Standard deviations in the simulations were <0.57% of normalization dose.

Tables

Generic image for table
TABLE I.

The incident electron beam parameters and their influence on dose distributions.

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/content/aapm/journal/medphys/39/1/10.1118/1.3668315
2011-12-09
2014-04-25
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Monte Carlo linear accelerator simulation of megavoltage photon beams: Independent determination of initial beam parameters
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/39/1/10.1118/1.3668315
10.1118/1.3668315
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