PURPOSE: To confirm the accuracy of the radiation dose at the isocenter by the standard linear accelerator-based stereotactic radiosurgery technique which was developed at Seoul National University Hospital. MATERIALS AND METHODS: Radiation dosimetry was undertaken during standard 5-arc radiosurgery using 6 MV X-ray beam from CL2100C linac. The treatment head was attached with circular tertiary collimators of 10 and 20 mm diameter. We measured the absorbed dose at the isocenter of a multi-purpose phantom using two kinds of detector : a 0.125 cc ionization chamber and a silicon diode detector. RESULTS: The dose differences at each arc plane between the planned dose and the measured dose at the isocenter raged from -0.73% to -2.69% with the 0.125 cc ion chamber, and from -1.29% to -2.91% with the diode detector during radiosurgery with the tertiary collimator of 20 mm diameter. Those with the 10-mm tertiary collimator ranged from -2.39% to -4.25% with the diode. CONCLUSION: The dose accuracy at the isocenter was +/-3%. Therefore, further efforts such as modification in processing of the archived image through DICOM3.0 format are required to lessen the dose difference.