1981 Volume 37 Issue 6 Pages 729-737
Fundamental study for radiation treatment planning using the electron density deduced from the CT number was described. In order to deduce the electron density of CT-5005 (EMI) wholebody image from the CT number, the following expressions were used : Es=(0.00339×CT number+3.39)×10^<23> for soft tissue such as lung, fat and muscle. Eh=(0.00120×CT number+3.34)×10^<23> for hard tissue such as bone. Dose calculation of the central axis depth dose was performed in a one field irradiation. For the correction of tissue inhomogeneity such as lung and bone, the pixel by pixel method was used. In this study, the following points were concluded. (1) The maximum difference between the electron density deduced from the CT number and the electron density produced from the technique of dual energy scanning or the theoretical method was within 2.3%. (2) In order to reduce the relative percent error of the central axis depth dose less than 2% at 10MV x-rays, the permitted limit of electron density error was 10% for the average electron density of the lung. But, if the relative percent error is permitted within 2%, the correction of tissue inhomogeneity was not necessary for the abdomen and the waist. (3) In order to reduce the relative percent error of the central axis depth less than 2% at 10MV x-rays, it was possible to deduce the original matrix size (256×320) into 64×80 matrix.
