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SU‐GG‐T‐225: Gantry‐Angle Dependence of a 2D Ion Chamber Array for IMAT QA

Publication ,  Conference
O'daniel, J; Kishore, M; Das, S; wu, QJ; Yoo, S; Yin, F
Published in: Medical Physics
January 1, 2010

Purpose: Gantry‐angle dependence of dose measurement for intensity‐modulated arc therapy (IMAT) quality assurance (QA) using a two‐dimensional ion chamber array may be significant. A new device, the gantry angle sensor, has been provided to compensate for this dependence. However, the default correction factors (CF) assume that the ion chamber angular response is symmetrical, uniform across all chambers, and independent of field size. Our goal was to test these three assumptions, and verify the use of the default CF. Method and Materials: The Matrixx ion chamber array (IBA Dosimetry, Inc.) was irradiated every 5° gantry rotation with a 27×27cm2 static field. The central ion chamber CF = calculation/measurement. To test the asymmetry, dose was delivered over 360°, and compared for symmetrical angles. To test for chamber response uniformity, CFs for off‐axis chambers were calculated and compared to the central ion chamber. To test for field size dependence, the dose delivery was repeated with 10×10cm2 and 2×2cm2 fields, and the central ion chamber CF recalculated. Results: The measured chamber response is asymmetrical with gantry angle. The median difference between the default and measured central ion chamber CFs is 1.2% (range: −0.3%–8.5%) from Gantry 0–180°, and 2.9% (range: 0.7%–7.6%) from Gantry 180–360°. The asymmetry appears to arise from both the device itself (median 1.4%, range 0.1%–3.4%) and from the device holder (median 1.7%, range 0.5%–4.8%). The central‐axis and peripheral CFs varied by up to 10%. There was no observed field size dependence at 10×10cm2, but differences of up to 4.7% were seen with the 2×2cm2 field.Conclusion: The CF table for gantry angle dependence of an ion chamber array should account for asymmetry, nonuniformity of chamber response, and field size effect for small fields. Clinics are recommended to verify their own CFs. © 2010, American Association of Physicists in Medicine. All rights reserved.

Duke Scholars

Published In

Medical Physics

DOI

ISSN

0094-2405

Publication Date

January 1, 2010

Volume

37

Issue

6

Start / End Page

3237

Related Subject Headings

  • Nuclear Medicine & Medical Imaging
  • 5105 Medical and biological physics
  • 4003 Biomedical engineering
  • 1112 Oncology and Carcinogenesis
  • 0903 Biomedical Engineering
  • 0299 Other Physical Sciences
 

Citation

APA
Chicago
ICMJE
MLA
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O’daniel, J., Kishore, M., Das, S., wu, Q. J., Yoo, S., & Yin, F. (2010). SU‐GG‐T‐225: Gantry‐Angle Dependence of a 2D Ion Chamber Array for IMAT QA. In Medical Physics (Vol. 37, p. 3237). https://doi.org/10.1118/1.3468616
O’daniel, J., M. Kishore, S. Das, Q. J. wu, S. Yoo, and F. Yin. “SU‐GG‐T‐225: Gantry‐Angle Dependence of a 2D Ion Chamber Array for IMAT QA.” In Medical Physics, 37:3237, 2010. https://doi.org/10.1118/1.3468616.
O’daniel J, Kishore M, Das S, wu QJ, Yoo S, Yin F. SU‐GG‐T‐225: Gantry‐Angle Dependence of a 2D Ion Chamber Array for IMAT QA. In: Medical Physics. 2010. p. 3237.
O’daniel, J., et al. “SU‐GG‐T‐225: Gantry‐Angle Dependence of a 2D Ion Chamber Array for IMAT QA.” Medical Physics, vol. 37, no. 6, 2010, p. 3237. Scopus, doi:10.1118/1.3468616.
O’daniel J, Kishore M, Das S, wu QJ, Yoo S, Yin F. SU‐GG‐T‐225: Gantry‐Angle Dependence of a 2D Ion Chamber Array for IMAT QA. Medical Physics. 2010. p. 3237.

Published In

Medical Physics

DOI

ISSN

0094-2405

Publication Date

January 1, 2010

Volume

37

Issue

6

Start / End Page

3237

Related Subject Headings

  • Nuclear Medicine & Medical Imaging
  • 5105 Medical and biological physics
  • 4003 Biomedical engineering
  • 1112 Oncology and Carcinogenesis
  • 0903 Biomedical Engineering
  • 0299 Other Physical Sciences