[en] In radiation therapy of the lung, it is difficult to decide an accurate tumor dose when only correcting for the density of the lung tissue. Many investigators have studied the correction of tumor dose in the lung. In this report, the mean density of the lung was measured by the transit dose and we calculated using the correction formula for tumor dose of the lung, devised by Burlin, Batho, and Dutreix, applied to the mean density of the lung. We compared these calculation results with a correction factor derived by measuring the lung phantom. It was proved that the method devised by Batho which calculates the correction factor on the basis on the tissue/air ratio, seems to be relatively accurate. (author)