Abstract
Summary The popular method of estimating tissue-air ratio was investigated by Onai et al. This is polynominal approximation for paramaters k and m which are expressed in Pfalzner's general formula. I made and approximation with three exponential functions for tissue-air ratio of cobalt 60 gamma radiation. It can be seen that. TAR [numerical formula] where l (cm) is one dimension of square filed, and d (cm) is the depth of interest. The result indicates that the errors are less than 2% in range of 0.5≤d≤20cm, 4≤l≤20cm
