Stereotactic radiosurgery of very small intracranial lesions or functional disorders is mainly delivered using a Gamma-Knife system (Elekta AB, Sweden) specifically designed for these clinical indications, but a conventional linac is also highly indicated for those treatments, provided that a quality assurance (QA) program including robust geometric tests is implemented [1,2]. The success of this one-session irradiation technique primarily relies on the control of the geometric accuracy of the irradiation.