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Original paper| Volume 77, P48-53, September 2020

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Determination of backscatter factors based on the quality index for diagnostic kilovoltage x-ray beams

  • Ryuki Tanabe
    Affiliations
    Graduate School of Health Sciences, Kumamoto University, 4-24-1 Kuhonji, Chuo-ku, Kumamoto 862-0976, Japan
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  • Fujio Araki
    Correspondence
    Corresponding author at: Department of Health Sciences, Faculty of Life Sciences, Kumamoto University, 4-24-1 Kuhonji, Chuo-ku, Kumamoto 862-0976, Japan.
    Affiliations
    Department of Health Sciences, Faculty of Life Sciences, Kumamoto University, 4-24-1 Kuhonji, Chuo-ku, Kumamoto 862-0976, Japan
    Search for articles by this author
Published:August 09, 2020DOI:https://doi.org/10.1016/j.ejmp.2020.07.032
Determination of backscatter factors based on the quality index for diagnostic kilovoltage x-ray beams
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      Highlights

      • •
        A correlation between backscatter factors, Bw, and Al-HVL was investigated using the quality index, QI as a parameter.
      • •
        Values of Bw for x-ray spectra were calculated from the weighted average of Bw for monoenergetic photons.
      • •
        The weighted averaged Bw for x-ray spectra agreed within 0.7% with those of direct Monte Carlo calculations.

      Abstract

      Purpose

      This study aims to investigate the relationship between backscatter factors and Al-half-value-layers (Al-HVL) by making the quality index (QI) a parameter for diagnostic kilovoltage x-ray beams.

      Methods

      Backscatter factors, Bw, for x-ray fluence spectra were calculated from the weighted average of Bw for monoenergetic photons of between 8 and 140 keV with field sizes of 10 cm × 10 cm to 40 cm × 40 cm. The value of Bw for monoenergetic photons was calculated from the ratio of the water kerma at the surface of a water phantom and that at the same point free-in-air using the EGSnrc/cavity code. The weighted averaged backscatter factors were validated by comparing them with those of direct Monte Carlo calculations for the x-ray fluence spectra. The Bw for the x-ray fluence spectra were classified by a QI of 0.35, 0.4, 0.5, 0.6, and 0.7 specified by the ratio of the effective energy and maximum energy. The relationship between Bw and Al-HVL was evaluated for the given QI values. The x-ray fluence spectra were generated for tube voltages of 40–140 kVp with Al-HVLs of 0.5–13.2 mm using the SpekCalc program.

      Results

      The weighted averaged backscatter factors for x-ray fluence spectra agreed within 0.7% with those of the direct Monte Carlo calculations. The backscatter factors were represented by the fitting curves of R2 > 0.99 with Al-HVL for the given QI values.

      Conclusions

      It is possible to obtain Bw more accurately by using QI specified by the measured Al-HVL.

      Keywords

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      Article info

      Publication history

      Published online: August 09, 2020
      Accepted: July 28, 2020
      Received in revised form: July 25, 2020
      Received: May 18, 2020

      Identification

      DOI: https://doi.org/10.1016/j.ejmp.2020.07.032

      Copyright

      © 2020 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

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