Page 48 - Fisica In Medicina n° 1/2017

^Äëíê~Åí=cáëáÅá= =Beam commissioning of a CyberKnife system with the unshielded diode PTW 60017, comparison with the microDiamond PTW 60019I. 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” - MessinaIntroductionThe Cyberknife system is a 6 MV LINAC mounted on a robotic arm specifically designed for SRS e SRBT treatments. The unflattened photon beam is collimated by a fixed and a variable collimation system with the same aperture(5-60 mm). Accurate dosimetry of small radiation fields used in all stereotactic applications can be made difficult because of loss of lateral electronic equilibrium, partial volume effect, detector perturbation and spectral change. Also, measurements are complicated by the dependence to physical properties of radiation detectors and by the inability, of some stereotactic system, to reproduce the reference conditions specified in the dosimetric protocol. All these problems must be considered during the CK commissioning executed using diode and microDiamond.Material and MethodsThe basic parameters for the commissioning CK system of RayTracing algorithm are the same as those used in the characterization of conventional field radiotherapy beams: TPRs, OCRs and OFs. These 3different parameters must be determined for all 12 aperture and for both the collimation system. The commissioning procedure was carried out using the unshielded p-type diode PTW 60017,particularly suitable for small field dosimetry thanks to its structural and physical characteristic. OCRs and OFs measurements were also performed with the PTW 60019 diamond.Results39