Page 77 - Fisica In Medicina n° 1/2017

^Äëíê~Åí=jÉÇáÅá= =CyberKnife SBRT for Non–Small Cell Lung Cancer using the Monte Carlo algorithmA. MICALI*, A. BROGNA*, C. SIRAGUSA*, I. BONAPARTE*, M. C. ANGIOCCHI*, F. MIDILI*, E. MONGELLI*, I. IELO**U.O.C. di Fisica Sanitaria – A.O.U. Policlinico “G. Martino” - MessinaIntroductionNon–Small Cell Lung Cancer (NSCLC) is often treated by Stererotactic Body Radiation Therapy (SBRT) using CyberKnife (CK). CK is a frameless image-guided radiosurgical system which delivers highly conformal treatment using a robot-mounted 6 MV compact linear accelerator. In this study, 10 treatment plans of lung tumors were calculated and compared with the two CK dose calculation algorithms: Ray Tracing (RT) and Monte Carlo (MC). MC is indicated as the "gold standard" of dose calculation algorithms. It predicts the absorbed dose by simulating the electron and photons transport and it takes into account the electronic disequilibrium due to tissues heterogeneity.Materials and MethodsFor each patient, a RT plan was computed with CT series (1,5 mm slice thickness) loaded into the TPS. Tumor doses of 60 Gy in 3 fractions or 23 Gy in single fraction were prescribed to primary tumors or metastasis, respectively. The clinical objective was to cover the 95% of the PTV volume with the prescribed dose. Using the same patient data, beam number, directions, weights, and monitor units, each RT plan was also re-calculated using the MC algorithm (1% uncertainty level) and the PTV coverage was evaluated. Finally, each MC plan was re-prescribed in order to reach a PTV coverage = 95% and cDVHs were compared.ResultsIn the overall comparison, MC plans with the same prescription isodose of the RT ones, show a PTV coverage always lower than that RT one: V100 [98.43-95.08]% vs. [59.46-83.90]% with RT and MC algorithm, respectively. In particular, peripherals lesions show the most considerable68