PROBLEM TO BE SOLVED: To reduce the calculation time to determine the optimum irradiation condition on the basis of an operator-set condition concerning an irradiation direction, prescription dose, etc. through repeated calculation.SOLUTION: On the basis of the distances between the axes of beams emitted to spots and calculation points, dose matrices A, B which are the contributions from beams emitted to irradiation positions to doses to the calculation points are divided into matrices AM, BM of doses which are to the calculation points falling within the target regions with the distance of the beam emitted to each spot from the beam axis being equal to or less than L and matrices AS, BS of doses which are to the calculation points falling within the target regions with the distance from the beam axis being greater than L, and d→S(1), d→S(2) containing the dose matrices AS, BS are regarded as constants at the time of repeated calculation. In addition, when an update condition is satisfied, objective functions are recalculated and updated using the values of the spot irradiation amount x→ and dose matrices A, B calculated at the time.COPYRIGHT: (C)2014,JPO&INPIT【課題】操作者が設定した照射方向や処方線量等に関する条件に基づき、最適な照射条件を反復計算により算出する際の計算時間を短縮する。【解決手段】スポットに照射したビームの軸と計算点との距離に基づき、照射位置に照射したビームから計算点への線量に関する寄与である線量行列A,Bを、各スポットに照射したビームのビーム軸からの距離がL以下の標的領域内の計算点への線量行列AM,BMと、ビーム軸からの距離がLより大きい標的領域内の計算点への線量行列AS,BSに分割するとともに、反復計算を行う際に、線量行列AS,BSを含むd→S(1),d→S(2)を定数とみなす。更に、更新条件を満たす場合は、その時点で算出されているスポット照射量x→と線量行列A,Bの値を用いて目的関数を再計算して更新する。【選択図】 図5
