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Constancy checks of well-type ionization chambers with external-beam radiation units.

Publication ,  Journal Article
Hackett, SL; Davis, B; Nixon, A; Wyatt, R
Published in: J Appl Clin Med Phys
November 8, 2015

Constancy checks of a well-type ionization chamber should be performed regularly as part of a quality assurance regime. The goal of this work was to test the feasibility of using a linear accelerator and an orthovoltage unit to check the constancy of a well-type chamber's response to an external radiation source. The reproducibility, linearity with dose, variation with dose-rate, and variation between energy-matched units of the well-type chamber response when exposed to 6 MV beams was examined. The robustness to errors in establishing the measurement conditions, including setting the source-to-surface distance and gantry angle, rotation of the chamber around the central axis of the beam, and the effect of changing the length of the chamber cable exposed to the field, were tested. The reproducibility and linearity with dose of the chamber response, and robustness to errors in establishing the measurement conditions for 100 kVp and 250 kVp beams from an orthovoltage unit, were also examined. The combined uncertainty, including contributions from errors in establishing the reference conditions, for well-type chamber measurements using a 6 MV beam from a linear accelerator is 1.0%. The combined uncertainties for measurements using 100 and 250 kVp beams were 1.8% and 1.5%, respectively. When focus-source distance errors were reduced to ≤ 1 mm, the combined uncertainties for the 100 and 250 kVp beams were 1.2% and 1.1%, respectively, when the dose to the chamber was confined to the linear region of the dose-response curve. The response of a well-type chamber should remain constant to within 1.2% when exposed to a constant dose from an external beam unit, if reference conditions can be reproducibly established. However, the uncertainty for establishing reference conditions for output measurements for an orthovoltage unit can be reduced, which would justify a reduction of the tolerance for constancy measurements.

Duke Scholars

Published In

J Appl Clin Med Phys

DOI

EISSN

1526-9914

Publication Date

November 8, 2015

Volume

16

Issue

6

Start / End Page

508 / 514

Location

United States

Related Subject Headings

  • Reproducibility of Results
  • Radiotherapy, High-Energy
  • Radiotherapy Dosage
  • Radiometry
  • Quality Assurance, Health Care
  • Particle Accelerators
  • Nuclear Medicine & Medical Imaging
  • Humans
  • Calibration
  • 5105 Medical and biological physics
 

Citation

APA
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ICMJE
MLA
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Hackett, S. L., Davis, B., Nixon, A., & Wyatt, R. (2015). Constancy checks of well-type ionization chambers with external-beam radiation units. J Appl Clin Med Phys, 16(6), 508–514. https://doi.org/10.1120/jacmp.v16i6.5608
Hackett, Sara L., Benjamin Davis, Andrew Nixon, and Ruth Wyatt. “Constancy checks of well-type ionization chambers with external-beam radiation units.J Appl Clin Med Phys 16, no. 6 (November 8, 2015): 508–14. https://doi.org/10.1120/jacmp.v16i6.5608.
Hackett SL, Davis B, Nixon A, Wyatt R. Constancy checks of well-type ionization chambers with external-beam radiation units. J Appl Clin Med Phys. 2015 Nov 8;16(6):508–14.
Hackett, Sara L., et al. “Constancy checks of well-type ionization chambers with external-beam radiation units.J Appl Clin Med Phys, vol. 16, no. 6, Nov. 2015, pp. 508–14. Pubmed, doi:10.1120/jacmp.v16i6.5608.
Hackett SL, Davis B, Nixon A, Wyatt R. Constancy checks of well-type ionization chambers with external-beam radiation units. J Appl Clin Med Phys. 2015 Nov 8;16(6):508–514.

Published In

J Appl Clin Med Phys

DOI

EISSN

1526-9914

Publication Date

November 8, 2015

Volume

16

Issue

6

Start / End Page

508 / 514

Location

United States

Related Subject Headings

  • Reproducibility of Results
  • Radiotherapy, High-Energy
  • Radiotherapy Dosage
  • Radiometry
  • Quality Assurance, Health Care
  • Particle Accelerators
  • Nuclear Medicine & Medical Imaging
  • Humans
  • Calibration
  • 5105 Medical and biological physics