PROBLEM TO BE SOLVED: To provide a dose calculation method and a dose calculation program capable of accurately calculating a dose in an outdoor space such as under the floor of a radiation irradiation room. A method for calculating a dose of an outdoor space b outside a shield a for shielding radiation provided around a radiation irradiation chamber having a radiation source S for irradiating radiation, wherein irradiation is performed from the radiation source S. It is assumed that at least a part of the radiation that has been transmitted through the shield a is scattered in the shield a and reaches a predetermined evaluation point E set in the outdoor space b, and the radiation is emitted from the radiation source S. The value of the contribution that the radiation scatters in the shield a and reaches the evaluation point E, and the multi-reflection in the outdoor space b outside the shield a after the radiation emitted from the radiation source S passes through the shield a. Then, the dose at the evaluation point E is obtained by adding the value of the contribution reaching the evaluation point E. [Selection diagram] Figure 1【課題】放射線照射室の床下などの室外空間の線量を精度良く計算することのできる線量計算方法、線量計算プログラムを提供する。【解決手段】放射線を照射する線源Ｓを有する放射線照射室の周囲に設けられた放射線遮蔽用の遮蔽体ａの外側の室外空間ｂの線量を計算する方法であって、線源Ｓから照射されて遮蔽体ａを透過する放射線のうち少なくとも一部が遮蔽体ａ内で散乱して、室外空間ｂ内に設定した所定の評価点Ｅに到達すると仮定して、線源Ｓから照射された放射線が遮蔽体ａ内で散乱して評価点Ｅに到達する寄与の値と、線源Ｓから照射された放射線が遮蔽体ａを透過した後に、遮蔽体ａの外側の室外空間ｂで多重反射して評価点Ｅに到達する寄与の値とを合算して評価点Ｅの線量を求めるようにする。【選択図】図１
