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

质子治疗计划的剂量计算方法已得到改进，以获得更准确的剂量预测。我们用幻影来验证准确性。研究发现，斜梁法比宽梁法更有效。改进了入射射束模型，以获得更准确的剂量预测。我们发展了一种距离调制的双波束方法（RMPBA），以减少计算时间的数量级，而保持精度。我们验证了笔形射束算法是有效的，以重现测量的剂量分布在水中的质子穿过材料，包括范围补偿器（=团）。与此相反，在横向不均匀性较大的介质中，发现铅笔束法的测量值和计算值之间存在明显的差异。产生差异的原因是笔形波束方法的散射模型不正确。蒙特卡罗计算是有效的，以改善这种情况。然而，使用GEANT3或LAHET等进行完整的Monet Carlo计算是耗时的。为了提高剂量分布的计算精度，我们采用了一种简化的蒙特卡罗（SMC）方法。据发现，减少计算时间是可能的SMC方法和并行处理，使用几个CPU将使剂量计算在30分钟内为现实的目标。总之，它是实用的笔形束算法的剂量计算与中等横向不均匀性沿着束路径的目标。对于沿着束流路径具有较大横向不均匀性的靶，强烈建议采用蒙特卡罗计算。

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.