Potential Efficacy of the Monte Carlo Dose Calculations of 6MV Flattening Filter-Free Photon Beam of M6^™ Cyberknife^® System

Retrospective MapCheck measurements of 50 patient’s treatment plans have suggested that MapCheck could be effectively employed in routine patient specific quality assurance in M6 Cyberknife with beams delivered at different treatment angles. However, for smaller MLCs segments (< 8 mm) a correction of (-4 %) was used to match the planned dose with MapCheck. To generalize this correction, a Monte Carlo (MC) simulation is required for such types of treatment plans. In doing so, MC simulations were performed for the M6 Cyberknife using the EGSnrc program. A total of 2-5 and 10-20 millions of incident particles histories in BEAMnrc and DOSXYZnrc, respectively were simulated. Preliminary results showed dose uncertainties ≤ 3% for all the standard fields (7.6 x 7.7 mm² to 100 x 100 mm²). During the simulation, an incident electron beam of 7 MeV with a FWHM of 2.2 mm was used to match with the stated nominal energy by comparing the simulation and corresponding measurement results. Good agreements for the dose profiles (≤ 2%) and dose outputs (≤ 3%) were found between the simulations and measurements at 800 mm Source to Axis Distance (SAD).