A CONVENIENT MULTIPLE SOURCE MODEL FOR VARIAN 2300C 6 MV-X BEAM BASED ON MONTE CARLO SIMULATED LINAC

Photon external radiotherapy of cancer takes advantage of the physical interaction of the photon and the secondary electron with biological tissue to kill cancer cells. The current linac is important equipment for producing an X-ray. The Monte Carlo method has been demonstrated to be the most accurate method for radiotherapy issues such as dose calculation and plan verification. However, its application in the clinic requires detailed information on the beam characteristics. A large quantity of the consumptive time for multiple simulation phases, such as linac treatment head simulation, beam trimmer module simulation, and patient/phantom simulation, and storage for the phase-space file (PSF), which records the information of the transported particle, are two knotty issues also. Therefore, a set of simple and convenient multiple source models (MSMs) including five sub-sources for regular fields from 3 X 3 cm to 30 X 30 cm was built, which is based on a VARIAN 2300C 6 MV-X beam simulated by the Monte Carlo code BEAMnrc and produced by BEAMnrc's beam characteristics analysis utility BEAMDP (BEAM Data Processor). This MSM reduced the three simulation phases to one to effectively decrease the consumptive time. The storage issue about the PSF was also solved for MSM's small volume. The dose distribution of the five-source model in a homogeneous phantom was compared with that of the full linac simulation and measurement data to verify reliability. The characteristics of the subsources were analyzed to present their feature. This work provided the base for implementing the Monte Carlo algorithm into the Accurate Radiotherapy System.