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Effects of tertiary MLC configuration on secondary neutron spectra from 18 MV x-ray beams for the Varian 21EX linear accelerator
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10.1118/1.3159301
/content/aapm/journal/medphys/36/9/10.1118/1.3159301
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/36/9/10.1118/1.3159301

Figures

Image of FIG. 1.
FIG. 1.

Schematic Monte Carlo model of the Varian 2100 linac showing neutron tally location at a source-to-axis distance of 100 cm and at a point 40 cm away from the gantry isocenter (in the inferior direction along the treatment couch). Measurements were made in the corresponding location.

Image of FIG. 2.
FIG. 2.

Unfolded neutron spectra measured in configurations 1 and 3.

Image of FIG. 3.
FIG. 3.

Neutron spectra measured in configurations 2 and 4.

Image of FIG. 4.
FIG. 4.

Neutron spectra measured in configurations 1 and 2.

Image of FIG. 5.
FIG. 5.

Measured spectrum and Monte Carlo calculated spectrum for configuration 1.

Image of FIG. 6.
FIG. 6.

Measured spectrum and Monte Carlo calculated spectrum for configuration 3.

Image of FIG. 7.
FIG. 7.

Measured photoneutron spectra for 18 MV photon beams for the Varian Clinac 21EX, Elekta Precise, and Siemens ONCOR linacs. Secondary neutron spectra for 18 MV photon beams for Siemens and Elekta spectra with the MLC and jaws closed and those for the Varian linac under two different conditions: Jaws closed and MLC closed (configuration 1) and jaws closed and MLC removed (configuration 3).

Tables

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TABLE I.

Collimator configurations (i.e., position of jaws and MLC) for the neutron spectrum measurements in this study.

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TABLE II.

Parameters calculated from the measured spectra for the four collimator configurations. Total uncertainties are shown to the right as percentages.

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TABLE III.

Quantitative comparison of the measured and calculated data for the four collimator configurations is presented in Table III, which shows the measured neutron fluence per MU, the average energy of the measured spectrum, and the ambient dose equivalent for each configuration.

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TABLE IV.

Absolute neutron production ( neutrons per source particle) for beamline components in each collimator configuration. Values in parentheses provide neutron production as a percentage of the net neutron production.

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TABLE V.

Our current measured photoneutron data and the measured and Monte Carlo calculated data of Kase et al. for a Varian linac operated at 18 MV beam energy (Refs. 3 and 11).

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/content/aapm/journal/medphys/36/9/10.1118/1.3159301
2009-08-12
2014-04-24
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Effects of tertiary MLC configuration on secondary neutron spectra from 18 MV x-ray beams for the Varian 21EX linear accelerator
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/36/9/10.1118/1.3159301
10.1118/1.3159301
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