Objective To investigate the application value of a transmission reference stealth ionization chamber in the relative dosimetry of stereotactic radiotherapy.Methods The relative dosage of Varian (R) Novalis 6 MV photon rays equipped with Brainlab (R) conical applicators was determined by two different approaches in the IBA (R) Blue Phantom.One approach was designed to utilize IBA (R) SFD3G semiconductor ionization chamber alone in the "step by step" measurement mode,whereas the other method was to utilize IBA (R) SFD as the field detector combined with stealth ionization chamber as the reference detector in the "continuous" measurement mode.The central axial percentage depth dose (PDD) and off axis ratio (OAR) in a diameter of 4 and 15 mm were measured and the time spent on each measurement was recorded.Results The PDDs at the central axis and OARs at a depth of 10 cm for both conical applicators were in good agreement between the two measurement approaches with a dose difference of＜ 1％.The time spent on PDDs and OARs measurement with stealth ionization chamber was shortened by 13.1％ and 20.7％ compared with those without Stealth ionization chamber.Conclusion Stealth ionization chamber can be applied in the retative dosimetry of stereotactic radiotherapy with high dose accuracy and high efficiency.