PROBLEM TO BE SOLVED: To reduce a difference between a numerical value, calculated by using CT number-water equivalent thickness conversion (calibration) in radiation therapy using an especially high CT number, and an actual measurement value and to highly accurately apply the CT number-water equivalent thickness conversion (calibration) in particle therapy using the high CT number.SOLUTION: The conversion apparatus for CT number-water equivalent thickness includes: a means for generating the diagram of CT number-water equivalent thickness to perform measurement changing a density for a variable density specimen, generating the diagram of CT number-water equivalent thickness in a moisture containing state and generating the diagram of CT number-water equivalent thickness in a dry state on a screen and a means for generating the calibration table of CT number-water equivalent thickness to constitute CT number data indicated by the diagram of CT number-water equivalent thickness in the moisture containing state in the state that the two diagrams are changed at the point of the high CT number and water equivalent thickness data corresponding to them as the calibration table of CT number-water equivalent thickness on the screen.COPYRIGHT: (C)2009,JPO&INPIT【課題】特に高CT値を用いる放射線治療用CT値-水等価厚変換(校正)を用いることにより算出した数値と実測値の差を小さくし、高CT値を用いる粒子線治療用CT値-水等価厚変換(校正)が精度高く適用可能であるようにした。【解決手段】画面の上に、可変密度試料について密度を変えて測定し、水分を含んだ状態でのCT値-水等価厚線図を生成させ、乾燥した状態でのCT値-水等価厚線図を生成させるCT値-水等価厚線図生成手段と、を備え、画面上で、前記二つの線図が高CT値の点で変わったときの状態の水分を含んだ状態でのCT値-水等価厚線図で表されるCT値データおよびこれに対応する水等価厚データをCT値-水等価厚校正テーブルとして構成するCT値-水等価厚校正テーブル生成手段を備える。【選択図】図1
