The Key Technologies And Application Of Medical Linear Accelerator And Patient Phantom Modeling Based On Monte Carlo Method

Radiotherapy is one of the three principal methods for cancer treatment, and dose calculation plays a key role in the treatment planning and verification. Nowadays Monte Carlo (MC) dose algorithms have been recognized as the most accurate technique for patient dose calculation, therefore the coupled modeling of medical linear accelerator and patient became one of the essential ingredients in the MC dose calculation for accurate radiotherapy.This work carried out the systematic investigation into the modeling of Linac treatment head, the multi-leaf collimator (MLC), and patient phantom and even furthers the coupled modeling of the above geometric structures. With those technical aspects, the main research contents and also innovation of this dissertation are briefly described as below:1. Based on the Multi-Physics Coupling Analysis Modeling program (SuperMC/MCAM), this study developed the method of Linac treatment head modeling based on the CAD model. A linear accelerator treatment head was modelling by Monte Carlo method. The MC-based model constructed for photon beams of6MeV was benchmarked against measurements in water phantom. The error between the calculation and the actual measurement was less than2%, and the Penumbra offset was less than3mm.2. A modeling method of multi-leaf collimator (MLC) was developed for accurate beam modeling of the irregular radiation fields in conformal or intensity modulated radiation therapy. The MLC leaf had the tongue-and-groove design to reduce inter-leaf radiation leakage, arid each leaf end is circular. The simulation of the inter-leaf leakage was less than2%. The MLC model was benchmarked by measurements in water phantom.3. A coupled modeling method of Linac treatment head, MLC, and patient phantom was developed based on the hierarchical geometry method, which solves the problem of different characterization of MC geometry and the problem of non-uniform coordinate system of MLC and patient phantom. The method was validated by simulated a clinic treatment plan and compared the results of calculation by EGSnrc, and the data was well coincident confirmed this method is valid.