A method of determining an actual, especially an actual effective, radiation dose distribution of a moving target volume includes detecting first and further positions of volume elements of the target volume in a first and at least one further motional state of the moving target volume, determining transformation parameters by transformation of the first positions into the further positions, irradiating the moving target volume in accordance with an irradiation plan which comprises a plurality of raster points 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, assigning raster points to subirradiation plans and determining the actual effective dose for each of the plurality of volume elements, in each case from contributions from the raster points of the subirradiation plans using the transformation parameters. Calculation and application of correction parameters which compensate for changes, caused by movement, to the position of the Bragg maximum and to the biologically effective dose applied.
