There is presented a phantom (734) comprising a matrix and a plurality of particles embedded in said matrix, wherein said particles comprise optically stimulated luminescence material, wherein a size of the phantom along each and all of the three geometrical dimensions is at least 10 millimetre. In an embodiment, an attenuation coefficient of the phantom is equal to or less than 10 cm -1 at a wavelength, where optical stimulation of the particles can be carried out at said wavelength and/or where stimulated luminescence takes place.