This is a radiolucent starburst interface used to attach Leksell Vantage Stereotactic System to table mounts from Imris.   

There are a number of different types of starburst adapters available for interfacing the Leksell®
Vantage Frame Holder with various OR table systems from many suppliers. Before starting the treatment preparations, make sure to check which starburst adapter that fits with the system that you plan to use. Both the starburst pattern and the screw thread must be compatible. Make sure the connecting screw can be fully tightened, rather than only turned a few times. The Vantage Starburst Adapters are marked with the name of the adapter, for identification.