A system to determine the isocenter of a LINAC includes apparatus and processes to determine the axis of rotation for the collimator, the gantry and the patient couch. The system and apparatus enable the tracking of the translation-rotation of mechanical components attached to the LINAC to compute the axis of rotation of Gantry, Collimator and Table. Based on the data collected related to these axis's the LINAC isocenter is determined. The apparatus utilized in the system includes a single emitter module, a signal receiver module, a positioning module. The system also includes a isocenter target module and a gravity module to determine a gravity vector for the LINAC.