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KMID : 0384620120230020114
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Korean Journal of Medical Physics
2012 Volume.23 No. 2 p.114 ~ p.122
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Practical Output Dosimetry with Undefined NdwCo-60 of Cylindrical Ionization Chamber forHigh Energy Photon Beams of Linear Accelerator
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Oh Young-Kee
Choi Tae-Jin
Song Ju-Young
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Abstract
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For the determination of absorbed dose to water from a linear accelerator photon beams, it needs a exposure calibration factor Nx or air kerma calibration factor Nk of air ionization chamber. We used the exposure calibration factor Nx to find the absorbed dose calibration factors of water in a reference source through the TG-21 and TRS-277 protocol. TG-21 used for determine the absorbed dose in accuracy, but it required complex calculations including the chamber dependent factors. The authors obtained the absorbed dose calibration factor Ndw Co-60 for reduce the complex calculations with unknown Ndw only with Nx or Nk calibration factor in a TM31010 (S/N 1055, 1057) ionization chambers. The results showed the uncertainty of calculated Ndw of IC-15 which was known the Nx and Ndw is within -0.6% in TG-21, but 1.0% in TRS-277. and TM31010 was compared the Ndw of SSDL to that of PSDL as shown the 0.4%, -2.8% uncertainty, respectively. The authors experimented with good agreement the calculated Ndw is reliable for cross check the discrepancy of the calibration factor with unknown that of TM31010 and IC-15 chamber.
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KEYWORD
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Exposure calculation factor Nx, Air kerma Nk, Absorbed dose calculation factor Ndw
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