Organ Doses and Effective Dose as a Function of Organ Depths under Body Surface for External Photon Exposure

A simplified method in which the equivalent doses in tissue or organs and effective dose for external photon exposure according to the ICRP 1990 Recommendations could be approximated by a single empirical expression is proposed. In this method, the position of an organ is assumed to be the main factor that determine its dose for external photon irradiation. Many organ depths with different body size for ages 1, 5, 10 years and adults were determined using the cross-sections of mathematical organ descriptions, and effective depth for approximating effective dose was obtained with the organ depths assigned to tissue weighting factors.Compared with the precised data for adults by the Monte Carlo method, the simple expression gives good approximates for most of deep organs and effective dose within about 20% except some organs, especially for lateral geometry. It was found that irradiation geometry affects the variations in age-dependent effective dose, and that the effective depths for ages 1, 5, 10 years, normalized to the adults depth, are directly proportional to the cubic root of the body weight. The usefulness of the concept of effective depth was also discussed with regard to the specified point of effective does in the body, obtained from the combination of the depths for the three typical geometries.