The invention relates to a treatment assessment device (37) for assessing a treatment of a subject, wherein a current treatment is tracked by a tracking unit (15, 30) and previous conformance values being indicative of previous degrees of conformance of previous treatments with previous treatment plans are provided. A visualization unit (34) generates a visualization being indicative of a current degree of conformance of the current treatment with the current treatment plan in relation to the previous degrees of conformance based on the tracking of the current treatment, the current treatment plan and the provided previous conformance values. The visualization can be shown on a display such that a physician can see how well the current treatment conforms to the treatment plan in comparison to the degree of conformance achieved in previous treatments, thereby providing an assessment of the quality of the current treatment in relation to previous treatments.