The invention relates to a scan region determining apparatus (12) for determining a scan region of a subject to be scanned by a scanning system (10) like a computed tomography system. A spatial transformation defining a registration of an overview image and a template image with respect to each other is determined, wherein initially the overview image and the template image are registered by using an element position indicator being indicative of a position of an element of the subject with respect to the overview image. A template scan region is defined with respect to the template image, wherein a final scan region is determined by projecting the template scan region onto the overview image by using the determined spatial transformation. The registration and thus the determination of the spatial transformation are very robust, which improves the quality of determining the final scan region.