Method and apparatus for irradiation of a moving target volume

Method of determining an actual radiation dose distribution in the case of irradiation of a moving target volume (102) which has a plurality of volume elements, having the following steps:

• detecting first positions of the plurality of volume elements in a first motional state of the moving target volume (102);
• detecting further positions of the plurality of volume elements in at least one further motional state of the moving target volume (102);
• determining transformation parameters by means of transformation of the first positions into the further positions;
• irradiating the moving target volume (102) in accordance with an irradiation plan having a plurality of raster points (222) to be irradiated, wherein during the irradiation of a raster point it is detected which of the motional states is occupied by the moving target volume (102);
• assigning raster points (222), during the irradiation of which the moving target volume (102) occupied the first motional state, to a first sub-irradiation plan;
• assigning raster points (222a), during the irradiation of which the moving target volume (102) occupied the at least one further motional state, to at least one further sub-irradiation plan;
• and
• determining the actual dose for at least one of the plurality of volume elements, in each case from contributions from the raster points (222, 222a) of the first sub-irradiation plan and of the at least one further sub-irradiation plan, using the transformation parameters.