LINAC-based radiosurgery has been commissioned at Mother Teresa University Hospital with the primary aim to treat the tumors, vascular lesions and functional disorders. Due to the size and shape of such targets, small cones are suitable for this technique. Measurements were made to characterize the dosimetric properties of small fields collimators set for PRIMUS Oncor Linac(Siemens). In addition, the geometric and dosimetric accuracy of linac was verified when used with Radionics planning

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... . Materials/Methods: A set of 12 cones (12.5-40.0mm diameter) was commissioned with the linac and modeled into the planning system Xknife for energies 6MV and 7MV flattening filter free. Output factors, TMRs and OARs were collected in PTW-MP3 water phantom, using PTW Pin point 0.016cm3 chamber. Isocenter position variations with table, gantry, and collimator rotation were found to be <0.5 mm, with a compounded accuracy of less than 1.0 mm. For TPS commissioning various verifications was performed: MU calculations accuracy, isocentre localization, output factors using OSL dosimetry by the IAEA and grafchromic films. Conclusions: Due to the difficulty of measuring small fields verifications and external audits were performed. The 6MV and 7MV FFF beams does not differ dosimetricaly much for small fields, but using FFF improves treatments delivery, reducing treatment times due to high dose rate. Our first clinical results are consistent and indicate a favorable evolution. They confirm that the combination of accuracy, conformity and homogeneity of this system makes it possible to apply safely single fractionated radiosurgery as a good alternative to selected patient