Stability of A-150 plastic ionization chamber response over a ~30 year period

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At the NIU Institute for Neutron Therapy at Fermilab, the clinical tissue-equivalent ionization chamber response is measured every treatment day using a cesium source that was configured to match readings obtained at the National Bureau of Standards. Daily measurements are performed in air using the air-to-tissue dose conversion factors given in AAPM Report no. 7. The measured exposure calibration factors have been tabulated and graphed as a function of time from 1978 to present. For A-150 plastic ionization chambers, these factors exhibit a sinusoidal variation with a period of approximately one year and amplitude of {+-} 1%. This variation, attributable ... continued below

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4 pages

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Kroc, Thomas K. & Lennox, Arlene J. August 1, 2007.

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At the NIU Institute for Neutron Therapy at Fermilab, the clinical tissue-equivalent ionization chamber response is measured every treatment day using a cesium source that was configured to match readings obtained at the National Bureau of Standards. Daily measurements are performed in air using the air-to-tissue dose conversion factors given in AAPM Report no. 7. The measured exposure calibration factors have been tabulated and graphed as a function of time from 1978 to present. For A-150 plastic ionization chambers, these factors exhibit a sinusoidal variation with a period of approximately one year and amplitude of {+-} 1%. This variation, attributable to the hygroscopic nature of A-150 plastic, is correlated with the relative humidity of the facility, and is greater than the humidity corrections for gas described in the literature. Our data suggest that chamber calibration should be performed at least weekly to accommodate these variations.

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  • Report No.: FERMILAB-PUB-07-418-AD
  • Grant Number: AC02-07CH11359
  • Office of Scientific & Technical Information Report Number: 914589
  • Archival Resource Key: ark:/67531/metadc888288

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  • August 1, 2007

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  • Sept. 22, 2016, 2:13 a.m.

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  • Sept. 26, 2017, 6:35 p.m.

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Kroc, Thomas K. & Lennox, Arlene J. Stability of A-150 plastic ionization chamber response over a ~30 year period, article, August 1, 2007; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc888288/: accessed June 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.