[Stereotactic radiosurgery using a linear accelerator (LINAC): simulation and positioning].

Stereotactic radiosurgery using a Gamma unit obtains good results for small intracranial diseases, arteriovenous malformation (AVM) and acoustic neurinoma. In stereotactic radiosurgery using a linear accelerator (LINAC), many fundamental problems are to be solved. 1) accuracy of a LINAC, 2) making the collimators for high energy X-ray narrow beams, 3) dosimetry for high energy X-ray narrow beams, 4) irradiation methods for stereotactic radiosurgery, 5) fixation of a patient's head and 6) simulation of a target. The usefulness of our method for simulation of a target and for positioning for radiosurgery was investigated. High energy X-ray narrow beams obtained with the collimators for narrow beams (field sizes: 9mm phi, 18mm phi and 27mm phi) satisfy clinical requirements for stereotactic radiosurgery, as indicated by dose profiles and isodose curves. No dosimetry method for high energy X-ray narrow beams has been established yet. Of the main irradiation methods for stereotactic radiosurgery, the method using multiple non-coplanar converging arcs needs no drastic reconstruction for use with LINAC. A patient's head was completely fixed by the stereotactic frame (Patil stereotaxic system or Leksell micro-stereotactic system). Simulation of a target was performed under CT scan. On CT image, the center of a target was determined and the three-dimensional coodinate on the stereotactic head frame target was settled so that the target would be reached. The three-dimensional coordinate for the target was coincided with the isocenter of a LINA by the laser beams of three-directional pointers. Afterwards, the target position was finely adjusted, by using the target positioner manipulator system.(ABSTRACT TRUNCATED AT 250 WORDS)