A method of obtaining the Awallcorrection factor of an ionization chamber in a60Co gamma -ray beam using tissue-air ratio data

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Abstract
A method is reported that evaluates the wall correction factor (Awall)water of an ionization chamber using measured data. The method needs a revised type of tissue-air ratio (TARcav) that should be measured with the ionization chamber. An experimental study has been carried out for 60Co gamma-rays using zero-area TARcav data extrapolated from non-zero-area TARcav data using the extrapolation method developed by Bjärngard and Petti. Using this technique, it is found that the value of (Awall)water for an ionization chamber has a deviation of -0.1% to -0.4% as compared with the Monte Carlo results. An experimental study has also been carried out using a published set of 60Co traditional tissue-air ratio (TAR) data assuming TARcav = TAR.