Research for high-accuracy dose calculation methods for proton treatment planning

点击翻译按钮获取中文摘要

Dose-calculation methods for proton treatment planning has been improved to obtain more accurate dose prediction. We used phantoms to verify the accuracies. Pencil beam methods were found to be more effective than the broad beam method. An incident beam model has been improved to obtain more accurate dose prediction. We developed a Range-Modulated Pencil Beam Method (RMPBA) to reduce the calculation time by an order of magnitude yet keeping the accuracy. We verified that the pencil beam algorithms are effective to reproduce measured dose distributions in water of protons traversing the material including a range compensator (=bolus). In contrast, noticeable discrepancies between measurements and calculations made by the pencil beam method were found in media with large lateral heterogeneities. The reason for the discrepancies is due to the incorrect scattering model of the pencil beam method. Monte Carlo calculations are effective to improve the situation. However, full Monet Carlo calculations using GEANT3 or LAHET, etc, are time-consuming. We applied a simplified Monte Carlo (SMC) method to improve the calculation accuracy of dose distributions. It is found that reduction of calculation time is possible by the SMC method and parallel processing using several CPUs will enable dose calculation for realistic targets within thirty minutes. In conclusion, it is practical to use the pencil beam algorithm for dose calculations for targets with moderate lateral heterogeneities along the beam paths. For targets with large lateral heterogeneities along the beam paths, Monte Carlo calculations are strongly recommended.