A multi-purpose object (100,200,300) for calibrating, monitoring and/or tracking a patient in a treatment system and/or a treatment planning system is described, the multi-purpose object being made of transparent material and defining an internal space having one or more targets, wherein an upper surface (106) is coated (110,130) so as to define a pattern of transparent markings (108). The interior of the multi-purpose object (100,200,300) can be back lit to present a high contrast surface image for a patient treatment, tracking or monitoring system
