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enables accurate confirmation of the isocenters of the gantry and couch. Considerable amount of time and effort were required for the quality control step, as 30 years ago, the accuracy of the LINAC system was suboptimal. Once the quality control procedures were complete, the SRS was started. The first case of SRS in Juntendo University involved a patient with cerebral arteriovenous malformation (AVM). The nidus position was analyzed by fusing the images from enhanced computed tomography (CT) and angiography. SRS was performed with five to six directions non-coplanar stereotactic multiple arc radiotherapy. Figure 3 shows a tung-Figure 2　Star shot before and after quality controlFigure 3　Tungsten collimator and attachment of Linac system for pencil beamsten collimator for converting X-rays to the pencil beam, which enabled the selection of an irradiation diameter from 5 mm to several centimeters according to the size of the target. After attaching the colli-mator to the LINAC system, the focused pencil beam X-rays irradiated the target. Two years after the SRS, the nidus had completely disappeared without complications (Figure 4).At that time, many cases of AVM were treated by SRS in Juntendo University. 30 cases of AVM were carried out in two and a half years. These cases were reported in the journal of the Japanese Society of Radiation Oncology. Of the 14 summa-461