Abstract: A special halo assembly is used with a stereotaxic device including a frame having four radiolucent substantially planar walls with radiopague indicia formed on the walls, and is operatively fixed to the frame walls by brackets to positively position the halo assembly in a predetermined position with respect to the walls. The frame is fixed with respect to a radiotherapy machine or a CT scanner. The halo assembly includes a number of brackets each having a first portion fixed to the ring component of the assembly, and a second substantially planar portion extending radially outwardly from the ring component. A method of practicing radiotherapy on a patient having a brain lesion or the like is accomplished utilizing the device. The halo assembly is surgically affixed to the patient's head to be maintained in place until all radiotherapy sessions for the patient are completed.