A system (30) to monitor a geometry of a treatment apparatus (31), an apparatus (51), a trackable assembly (43), program product (81), and methods are provided. The system (30) includes a treatment apparatus (31) having a radiation emitter (33), a rotating assembly (35) controlled by a controller (39), and an application computer (41), which provides treatment delivery instructions to the controller (39). The system (30) can also include a trackable assembly (43) connected to the rotating assembly (35) and having a fixedly connected first trackable body (45) which functions as a reference fixture and a pivotally connected second trackable body (49) which provides data used to determine a rotation angle of the rotating assembly (35). The sys...
