[Improvement of the first cerebral stereotactic radiosurgery system of Hungary]

The first cerebral stereotactic radiosurgery system in Hungary was built in 1991. This system was based on a Leksell stereotactic head frame and a Neptun 10p linear accelerator. We performed 624 radiosurgery treatments with this system between 1991 and 2000. Our objective was to increase the reliability of operation and to extend the applicability of our radiosurgery system.

We modified our stereotactic floor stand with specially designed adapter plates to make it compatible with the Mevatron KD and Neptun 10p linear accelerators and other stereotactic head frames (Riechert-Mundiger, CRW and BrainLab). We made a new tertiary collimator holder attachable to the Mevatron KD linac. The range of treatable cerebral lesion was increased from 10-30 mm to 5-42.5 mm with additional collimator inserts. With the above modifications our radiosurgery system is compatible simultaneously with the Neptun 10p and the Mevatron KD linear accelerators. This way we were able to increase the reliability of operation of the system, as the treatment can be performed with the Neptun 10p linac in case of breakdown of the Mevatron KD linac after fixation of the head frame to a patient's skull.

The measured diameter of the radiation isocenter defined by the new radiosurgery collimator was less than 1 mm with the Mevatron KD linac. According to the Lutz-test the distance between the radiosurgery isocenter and the rotation axis of ZIV treatment table was less than 0.5 mm. Results of phantom test showed that the overall spatial precision of our modified radiosurgery system was better than 1.3 mm with Leksell head frame.

On the basis of experiences with 662 patients' radiosurgery treatments, the extension of our first cerebral radiosurgery system to Mevatron KD linear accelerator resulted in a more reliable operation. In accordance with our phantom tests the extension of the original system did not worsen its overall spatial precision.