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KMID : 1001220100120010051
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Journal of the Korean Society of Digital Medical Imaging Technology
2010 Volume.12 No. 1 p.51 ~ p.58
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Stem Effect Correction Factor of Ionization Chamber in Exposure Measurements of High Energy Photons
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Park Cheol-Woo
Lee Jae-Seung
Kweon Dae-Cheol
Cha Dong-Soo
Kim Jin-Soo
Kim Kyoung-Keun
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Abstract
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Ionization chambers often exhibit a stem effect, caused by interactions of radiation with air near the chamber end, or with dielectric in the chamber stem or cable. In this study measured stem effect correction factor for length of ionization chamber from medical linear accelerator recommend to with the use of stem correction method. For a model of the Farmer-type chamber, were used to calculate the beam quality correction factor. These interactions contribute to the apparent measured exposure. Additionally, it needs to consider ionization chamber use of small volume and stem effect of cable by a large field. Linear accelerator generated photons energy and increased dose repeatedly measured by using stem correction method. Stem effect was dependence of the energy and increases with photon energy conditions improved of beam quality. In conclusion, stem effect correction factor was measured within 0.4% calculated according to the exposures stem length and also supposed to determined below 1% of another stem correction method.
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KEYWORD
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Ionization chamber, Stem effect, Correction factor, Linear accelerator
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