A data processing method for determining an assessment of a candidate treatment plan, the candidate treatment plan being a plan for treatment of a patient's body, the data processing method comprising the following steps which are all performed by a computer: acquiring assessment criteria data describing criteria for assessing a treatment plan to be assessed and referred to as assessable treatment plan; automatically determining virtual patient data based on a simulation of a plurality of virtual surgical treatments of the patient by determining the effect of the virtual surgical treatment of the patient on current patient data, the virtual surgical treatments comprising resection of parts of a target region of the patient's body, the target region comprising a tumour and the virtual patient data describing the anatomical structure of the target region and the virtual surgical treatments defining a minimum boundary surface for a minimum resection and a maximum boundary surface for a maximum resection, wherein the plurality of virtual surgical treatments are determined based on an elastic fusion which elastically transforms the shape of the target region defined by the minimum boundary surface into the shape of the target region defined by the maximum boundary surface by interpolating between the minimum boundary surface and the maximum boundary surface; automatically determining candidate treatment plan data on the basis of the virtual patient data, the candidate treatment plan data describing the candidate treatment plan, the candidate treatment plan describing a treatment plan for a virtual radiotherapy treatment of the target region to be performed after the virtual surgical treatment; and automatically determining the assessment of the candidate treatment plan on the basis of the determined virtual patient data, the assessment criteria data, and the candidate treatment plan data. acquiring assessment criteria data describing criteria for assessing a treatment plan to be assessed and referred to as assessable treatment plan; automatically determining virtual patient data based on a simulation of a plurality of virtual surgical treatments of the patient by determining the effect of the virtual surgical treatment of the patient on current patient data, the virtual surgical treatments comprising resection of parts of a target region of the patient's body, the target region comprising a tumour and the virtual patient data describing the anatomical structure of the target region and the virtual surgical treatments defining a minimum boundary surface for a minimum resection and a maximum boundary surface for a maximum resection, wherein the plurality of virtual surgical treatments are determined based on an elastic fusion which elastically transforms the shape of the target region defined by the minimum boundary surface into the shape of the target region defined by the maximum boundary surface by interpolating between the minimum boundary surface and the maximum boundary surface; automatically determining candidate treatment plan data on the basis of the virtual patient data, the candidate treatment plan data describing the candidate treatment plan, the candidate treatment plan describing a treatment plan for a virtual radiotherapy treatment of the target region to be performed after the virtual surgical treatment; and automatically determining the assessment of the candidate treatment plan on the basis of the determined virtual patient data, the assessment criteria data, and the candidate treatment plan data.