Thermal and temporal response of ionization chambers in radiation dosimetry

Indra J. Das, Timothy C. Zhu

Research output: Contribution to journalArticle

9 Scopus citations

Abstract

The temporal and thermal response of various commonly used ion chambers (NEL, Exradin, PTW) with different wall and electrode materials is studied in a water phantom. Measurements were taken in heating water bath having an automatic temperature control mechanism. All chambers were submersed at 3 cm depth in water phantom and connected to separate electrometers for simultaneous readings for a given dose from a 6 MV beam. The temporal response was studied at approximately ± 10 °C from room temperature, i.e., 10 °C and 30°C. Temporal results show that all chambers reach quick equilibrium response within <2 minutes of submersion in water. The steady-state thermal response was dependent upon the water temperature and wall and electrode compositions. The temperature and pressure corrected response of the NEL chamber was least affected by the changes in water temperature, where as the Exradin chamber has positive and PTW has negative slope with water temperature. The response varied within ±1.5% between 10 °C-50 °C temperature and is mainly dependent on volume changes rather than the humidity. A correction factor based on thermal coefficients is derived for each chamber. It is concluded that ion chamber correction factors can be divided into first order; temperature and pressure connection, second order; volume correction for thermal expansion, and third order; humidity correction. To eliminate dosimetric error, the temporal and thermal response should be known for a chamber or water phantom temperature should be maintained close to room temperature.

Original languageEnglish (US)
Pages (from-to)573-578
Number of pages6
JournalMedical Physics
Volume31
Issue number3
DOIs
StatePublished - Mar 2004

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Keywords

  • Dosimetry
  • Humidity correction
  • Ion chamber
  • Temporal response
  • Thermal response

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging

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