Quantifying the effect of off-focal radiation on the output of kilovoltage x-ray systems

Ali, E S. M.; Rogers, D W. O.

doi:10.1118/1.2966348

Title: Quantifying the effect of off-focal radiation on the output of kilovoltage x-ray systems

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Abstract

In a typical x-ray tube, off-focal radiation is mainly generated by the backscattered electrons that reenter the anode outside the focal spot. In this study, BEAMnrc (an EGSnrc user-code) is modified to simulate off-focal radiation. The modified BEAMnrc code is used to study the characteristics of electrons that backscatter from the anode, and to quantify their effect on the output of typical x-ray systems. Results show that the first generation backscatter coefficient is {approx}50% for tungsten anodes at diagnostic energies, and {approx}38% for molybdenum anodes at mammography energies. Second and higher generations of backscatter have a relatively minor contribution. At the patient plane, our simulation results are in excellent agreement with experimental measurements in the literature for the spectral shape of both the primary and the off-focal components, and also for the integral off-focal-to-primary ratio. The spectrum of the off-focal component at the patient plane is softer than the primary, which causes a slight softening in the overall spectrum. For typical x-ray systems, the off-focal component increases patient exposure (for a given number of incident primary electrons) by up to 11% and reduces the half-value layer and the effective energy of the average spectrum by up to 7% and 3%,more »« less

Authors:

Ali, E S. M.; Rogers, D W. O. ^[1]

Carleton Laboratory for Radiotherapy Physics, Ottawa Carleton Institute for Physics, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6 (Canada)

Publication Date:: Mon Sep 15 00:00:00 EDT 2008

OSTI Identifier:: 21120920

Resource Type:: Journal Article

Journal Name:: Medical Physics

Additional Journal Information:: Journal Volume: 35; Journal Issue: 9; Other Information: DOI: 10.1118/1.2966348; (c) 2008 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0094-2405

Country of Publication:: United States

Language:: English

Subject:: 62 RADIOLOGY AND NUCLEAR MEDICINE; ANODES; BACKSCATTERING; BIOMEDICAL RADIOGRAPHY; CATHODES; COMPUTERIZED SIMULATION; MAMMARY GLANDS; MOLYBDENUM; MONTE CARLO METHOD; PATIENTS; SPECTRA; TUNGSTEN; X-RAY TUBES

Citation Formats


                    Ali, E S. M., and Rogers, D W. O. Quantifying the effect of off-focal radiation on the output of kilovoltage x-ray systems.  United States: N. p., 2008. 
        Web.  doi:10.1118/1.2966348.

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                    Ali, E S. M., & Rogers, D W. O. Quantifying the effect of off-focal radiation on the output of kilovoltage x-ray systems.  United States.  https://doi.org/10.1118/1.2966348

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                    Ali, E S. M., and Rogers, D W. O. 2008.  
        "Quantifying the effect of off-focal radiation on the output of kilovoltage x-ray systems".  United States.  https://doi.org/10.1118/1.2966348.

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@article{osti_21120920,

  title        = {Quantifying the effect of off-focal radiation on the output of kilovoltage x-ray systems},

  author       = {Ali, E S. M. and Rogers, D W. O.},

  abstractNote = {In a typical x-ray tube, off-focal radiation is mainly generated by the backscattered electrons that reenter the anode outside the focal spot. In this study, BEAMnrc (an EGSnrc user-code) is modified to simulate off-focal radiation. The modified BEAMnrc code is used to study the characteristics of electrons that backscatter from the anode, and to quantify their effect on the output of typical x-ray systems. Results show that the first generation backscatter coefficient is {approx}50% for tungsten anodes at diagnostic energies, and {approx}38% for molybdenum anodes at mammography energies. Second and higher generations of backscatter have a relatively minor contribution. At the patient plane, our simulation results are in excellent agreement with experimental measurements in the literature for the spectral shape of both the primary and the off-focal components, and also for the integral off-focal-to-primary ratio. The spectrum of the off-focal component at the patient plane is softer than the primary, which causes a slight softening in the overall spectrum. For typical x-ray systems, the off-focal component increases patient exposure (for a given number of incident primary electrons) by up to 11% and reduces the half-value layer and the effective energy of the average spectrum by up to 7% and 3%, respectively. The larger effects are for grounded cathode tubes, smaller interelectrode distance, higher tube voltage, lighter filtration, and less collimation. Simulation time increases by {approx}30% when the off-focal radiation is included, but the overall simulation time remains of the order of a few minutes. This study concludes that the off-focal radiation can have a non-negligible effect on the output parameters of x-ray systems and that it should be included in x-ray tube simulations for more realistic modeling of these systems.},

  doi          = {10.1118/1.2966348},

  url          = {https://www.osti.gov/biblio/21120920},
  journal      = {Medical Physics},

  issn         = {0094-2405},

  number       = 9,

  volume       = 35,

  place        = {United States},

  year         = {Mon Sep 15 00:00:00 EDT 2008},

  month        = {Mon Sep 15 00:00:00 EDT 2008}

}

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