Abstract: An assembly is provided which is capable of the multiple functions that are necessary for the quality control of teleradiotherapy machines such a high energy medical accelerators, cobalt 60 machines, and low energy x-ray machines. The assembly includes a detector which is isocentrically rotatable about a pair of horizontal axes. Photodetectors or a luminescent screen are provided within the detector for detecting light and/or radiation. Tests which may be performed with the assembly include determining the position and size of a light field, the mechanical isocentricity of the gantry and of the collimator, positioning of the lasers in the treatment room, the optical distance indicator, and coincidence, symmetry, flatness and uniformity of the radiation and light fields. The multifunctionality of the assembly is based upon the isocentricity of the detector, this invariant point in space being positioned to coincide with that of the treatment machine.