A three-dimensional CT value data acquisition unit 36, a prescription data input processing unit 32 for acquiring prescription data, and a stopping power ratio conversion for generating first conversion data 41 and second conversion data 42 based on the three-dimensional CT value data Unit 37 and nuclear reaction effective density conversion unit 38, and a calculation unit 33 for obtaining a dose distribution based on the prescription data, the first conversion data 41 and the second conversion data 42, and the stopping power ratio conversion unit 37 and The nuclear reaction effective density conversion unit 38 executes a correction process for correcting data obtained from the three-dimensional CT value data using a physical quantity indicating how easy the particles of the charged particle beam 3 that are incident are to be crushed. An irradiation planning device having a configuration for obtaining the dose distribution is provided. As a result, in calculating the dose distribution in the body in the particle beam irradiation plan, the dose error caused by the difference in the nuclear reaction probability caused by the incident particles in the body from the probability of the nuclear reaction caused in water is easily and accurately corrected .３次元ＣＴ値データ取得部３６と、処方データを取得する処方データ入力処理部３２と、第１変換データ４１および第２変換データ４２を前記３次元ＣＴ値データに基づいて作成する阻止能比変換部３７および核反応実効密度変換部３８と、前記処方データと前記第１変換データ４１および第２変換データ４２に基づいて線量分布を求める演算部３３とを備え、前記阻止能比変換部３７および核反応実効密度変換部３８は、入射した前記荷電粒子ビーム３の粒子をどれだけ砕きやすいかを示す物理量を用いて前記３次元ＣＴ値データにより得られるデータを補正する補正処理を実行した上で前記線量分布を求める構成である照射計画装置を提供する。これにより、粒子線照射計画における体内での線量分布の計算において、入射粒子が体内で起こす核反応確率が水中で起こす核反応確率と異なることに起因する線量誤差を、簡便かつ高精度に補正する。
