In planning of radiation therapy treatment of at least one structure in a region of a patient body, a first treatment plan is generated on the basis of a planning image of the body region and on the basis of dose objectives. A further image of the body region of the patient body is received, and a transformation is determined for generating an adapted treatment plan from the first treatment plan and/or for generating an adapted dose distribution from the dose distribution corresponding to the first treatment plan on the basis of the further image and determines an adapted treatment plan on the basis of the transformation and/or the adapted dose distribution. The transformation on the basis of the dose objectives. In adapting the dose distribution, an efficient iterative dosimetric patient setup optimization may be employed to reduce the dose computations.