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Polarity effect in commercial ionization chambers used in photon beams with small fields

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Abstract

Ionization chambers are the instruments of choice for use in photon dosimetry. Ionization chambers together with radiographic films represent the best detectors for measurement of dose distribution for a quality assurance (QA) program in intensity-modulated radiotheraphy (IMRT). The polarity effect was investigated for seven different commercially available ionization chambers. This study concentrated on measuring the dependence of the polarity effect at various energies, and for various field size, ionization chamber, and electrometer combinations. Of the seven chambers, CC01, PTW23323, and PTW31006 had the largest polarity effect for small field sizes. The materials of the central electrode of these three chambers were steel or air-equivalent plastic C-552. The magnitude of the polarity effect was shown to be strongly dependent on the material of the collecting electrode. This polarity effect dependence was observed for the ionization chambers and small field sizes studied.

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Acknowledgments

The authors would like to thank the Editorial Assistant for initial polishing, and also the Reviewer, Associate Editor and Deputy Editor of Radiological Physics and Technology for providing us excellent assistance and advice. The authors are indebted to the radiological technologists of the Hoshigaoka Koseinenkin Hospital for technical assistance in preparing the manuscript.

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Authors and Affiliations

  1. Department of Radiology, Hoshigaoka Koseinenkin Hospital, 4-8-1 Hoshigaoka, Hirakata, Osaka, 573-0013, Japan

    Tetsunori Shimono, Hiroshi Takahashi & Hiroshi Okuda

  2. Department of Quantum Medical Technology, Kanazawa University Graduate School of Medical Sciences, 5-11-80 Kodatsuno, Kanazawa, Ishikawa, 920-0942, Japan

    Kichiro Koshida & Kosuke Matsubara

  3. Department of Radiology, Nara Hospital Kinki University Medical School, 1248-1 Otoda, Ikoma, Nara, 630-0293, Japan

    Hidekazu Nambu

Authors
  1. Tetsunori Shimono
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  2. Kichiro Koshida
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  3. Hidekazu Nambu
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  4. Kosuke Matsubara
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  5. Hiroshi Takahashi
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  6. Hiroshi Okuda
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Correspondence to Tetsunori Shimono.

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Shimono, T., Koshida, K., Nambu, H. et al. Polarity effect in commercial ionization chambers used in photon beams with small fields. Radiol Phys Technol 2, 97–103 (2009). https://doi.org/10.1007/s12194-008-0050-1

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  • DOI: https://doi.org/10.1007/s12194-008-0050-1

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