On the correlation between specified depth dose and effective dose

The aim of this study was to find a single best location in the body to relate the dose equivalent of the point to the effective dose, faithfully based on the basic concept of effective dose which requires many organ doses assigned tissue weighting factors in estimating it. To obtain the specified depth numerically close to the effective dose, the least squares fits were applied between tissue-depth dose data computed by Saito for the model of a tissue equivalent slab and the effective dose for the photon energy range of 15 keV to 10 MeV. With the specified depth, the experiments using the PMMA phantom manufactured to place a TLD badge without an envelope at the specified depth were performed. The specific depths were found to be 8 cm for AP geometry, 12 cm for PA and 18 cm for LAT; the results are similar to the effective depths derived from the simplified empirical expression for the approximate of organ and effective dose. The idea of this method can also be applied to experimentally evaluate the effective dose by using anthropomorphic RANDO phantom, in the simplest way, such as the cases where a reestimation of the real exposure is necessary. (N.K.)