HISTOGRAM BASED BREMSSTRAHLUNG RADIATION SOURCE MODEL FOR THE CYBERKNIFE MEDICAL LINEAR ACCELERATOR

The accuracy of dose calculations is of fundamental importance in treatment planning of radiation therapy. The dose distributions must be calculated and verified by an accurate algorithm. The Monte Carlo simulation (statistical method, based on random sampling) of radiation transport is the only method that makes it possible to perform high-precision dose calculations in the case of a complex geometry. The main bottleneck for the application of this method in practical planning of radiation therapy is the lack of a general virtual source model of the accelerator radiation source. There are several approaches that have been described in the literature [1]. The goal of this work is to build a source model, based on histogram distributions, to represent the 6 MV photon beams from the CyberKnife stereotactic radiosurgery system [2] for Monte Carlo treatment planning dose calculations. The transport of particles in treatment head of CyberKnife was simulated. Energy, radial and angular distributions were calculated. Source model was created on the base of the cumulative histograms. This approach provides producing an unlimited number of particles for the next dosimetric planning. Results of source modelling were verified in comparison with full-scale simulation without model. Good agreement was shown with calculations using the source model of the linear accelerator treatment head.