Multi-objective optimization of inverse planning for accurate radiotherapy

The multi-objective optimization of inverse planning based on the Pareto solution set, according to the multi-objective character of inverse planning in accurate radiotherapy, was studied in this paper. Firstly, the clinical requirements of a treatment plan were transformed into a multi-objective optimization problem with multiple constraints. Then, the fast and elitist multi-objective Non-dominated Sorting Genetic Algorithm （NSGA-） was introduced to optimize the problem. A clinical example was tested using this method. The results show that an obtained set of non-dominated solutions were uniformly distributed and the corresponding dose distribution of each solution not only approached the expected dose distribution, but also met the dosevolume constraints. It was indicated that the clinical requirements were better satisfied using the method and the planner could select the optimal treatment plan from the non-dominated solution set.

Photon Dose Calculation Method Based on Monte Carlo Finite-Size Pencil Beam Model in Accurate Radiotherapy

This study mainly focused on the key technologies,the photon dose calculation based on the Monte Carlo Finite-Size Pencil Beam(MCFSPB)model in the Accurate Radiotherapy System(ARTS).In the MCFSPB model,the acquisition of pencil beam kernel is one of the most important technologies.In this study,by analyzing the demerits of the clinical pencil beam dose calculation methods,a new pencil beam kernel model was developed based on the Monte Carlo(MC)simulation and the technology of medical accelerator energy spectrum reconstruction.which greatly improved the accuracy of calculated result.According to the axial symmetry principle,only part of simulation results was used for the data of pencil beam kernel,which greatly reduced the data quantity of the pencil beam and reduced calculated time.Based on the above studies,the MCFSPB method was designed and implemented by the Visual C++development tool.With several tests including the comparisons among the American Association of Physicists in Medicine(AAPM)No.55 Report sample and the ion chamber measurement of lung-simulating inhomogeneous phantom in clinical treatment plan,the results showed that the maximum error of most calculated point was less than 0.5%in the homogeneous phantom and less than 3%in the heterogeneous phantom.This method met the clinical criteria,and would be expected to be used as a fast and accurate dose engine for clinic TPS.