The electron density is one of the most important element for thetreatment planning in the radiotherapy, because this information isused for the range estimation of the heavy-ion beam. Although theelectron density has been converted from CT number obtained byconventional x-ray computed tomography(CT) at present, it is notenough for the more detailed planning due to uncertainties that arisefrom the beam hardening effect and the conversion process. In order totake more accurate electron density, we have developed the dual-energyx-ray CT system using the synchrotron radiation. The dual-energy x-rayCT has no influence of the beam hardening because of scanning usingmonochromatic x-rays. The experiments were carried out using twomonochromatic x-rays at the monochromatic beam-lines in KEK-AR andSPring-8. As the result, it was succeeded that the electron densitiesby the dual-energy x-ray CT were agreement with the theoretical valueswith the accuracy less than 1% for some materials. In addition, as theapplication for more practical use in diagnostics, the CT using themixture of main and harmonics x-rays produced by the monochromator hasbeen investigated. From the preliminary experiments, it was found thatthe accuracy was as same as that by dual-energy x-ray CT. We willdescribe the dual-energy x-ray CT system and discuss thequantitativity and the image characteristic for this system.Eighth International Conference on Synchrotron Radiation Instrumentatio
