[Technique of Linac radiosurgery for cerebral arteriovenous malformations]

Description of the irradiation technique used by our group since 1986 for radiosurgery of cerebral arteriovenous malformations using Xrays minibeams from a linear accelerator. Method. The technique was elaborated by O. Betti in the early 80. He used several coronal arcs to irradiate the center of the target with X rays circular minibeams. Their diameter (6 to 20 mm) is chosen according to the size of the nidus. The patient is seated in a specially built armchair. His head is immobilized with the Talairach frame afixed in the calvarium by 4 special screws: they allow to remove the frame after stereotactic angiography and/or CTscan and to replace it to perform the stereotactic irradiation. The frame and the head rotate around an horizontal axis passing by the linac isocenter ie the center of the target volume. The combination of both movements: rotation of the Linac and rotation of the stereotactic frame covers a spherical sector representing the surface of portals of entry of the minibeams. The frame can slide on a plate allowing access to the entire brain. Results. The special seat and the frame are movable on curved rails allowing to avoid or reduce irradiation of the body of the patient.

We have been using this system of irradiation in the seated position since 1986 to treat more than 900 patients.