Page 46 - Fisica In Medicina n° 1/2017

^Äëíê~Åí=cáëáÅá= =Small Field Dosimetry: CyberKnife OFs comparison between different detectors and clinical applicationsI. BONAPARTE*, C. SIRAGUSA*, A. BROGNA*, A. MICALI*, M. C. ANGIOCCHI*, F. MIDILI*, E. MONGELLI*, I.IELO**U.O.C. di Fisica Sanitaria – A.O.U. Policlinico “G. Martino” - MessinaIntroductionCyberKnife (CK) is an image-guided frameless radiosurgery system capable to deliver single or fractionated treatments. It consists of a 6 MV Flattening Filter Free LINAC mounted on a robotic manipulator with two collimation systems, Fixed and IRIS (12 small fields available for each: 5-60 mm). The dimensions of these small fields require high accurate geometrical and dosimetric beam characterization. In particular, Output Factors (OFs) should be modified through Monte Carlo (MC) correction factors (Francescon et al.). The aim of this work was to compare treatment plans calculated with raw and corrected OFs measured with an unshielded PTW 60017 diode. Moreover corrected OFs were compared to raw PTW 60019 microDiamond ones.Materials and MethodsThe PTW 60017 is a waterproof p-type silicon diode detector with a sensitive volume of 0.03 mm3 and a 0,6 mm radius circular active layer. The PTW 60019 is a waterproof diamond detector 1 mm thick, with a sensitive volume of 0.004 mm3 and a 1,1 mm radius. OFs measurement were performed in water for both the collimation systems at different SAD (650-800-1000) mm and at 15 mm depth. MC correction factors were applied to raw diode measurements for fields less than 15 mm. Corrected silicon diode OFs were compared to the rough diamond ones. Finally 10 trigeminal neuralgia treatment plans were calculated with raw and corrected diode OFs sets using the CK trigeminal path. A dose of 58 Gy in single fraction was prescribed to the target with a maximum dose of 9-10 Gy to the brain stem.Results37