均匀磁场下碳离子笔形束的剂量变化分析及位置修正方法

Dose Variation Analysis and Position Correction Method for Carbon-ion Pencil Beams under Uniform Magnetic Fields

分析外加均匀磁场对于碳离子笔形束剂量分布的影响,并考虑修正这种影响,为磁共振成像引导碳离子放射治疗的临床应用提供指导。本文利用蒙特卡罗方法模拟计算了不同能量碳离子笔形束在不同强度磁场下的剂量分布情况,发现垂直于碳离子束入射方向的均匀磁场对于碳离子笔形束射程缩短的影响很小,磁场对碳离子束的主要影响是引起束流横向偏转,特别是碳离子束布拉格峰位置的横向侧移。横向侧移程度与碳离子束的能量和磁场强度相关,根据模拟结果,得到了一个计算碳离子束布拉格峰在磁场中相对横向偏转的方程,并提出一种校正外加磁场引起的碳离子束布拉格峰横移的角度修正方法。这些结果可用于指导磁共振图像引导碳离子放射治疗计划系统的研发。

The influence of uniform magnetic fields on the dose distribution of carbon-ion pencil beams is analyzed,and the influencing effect is corrected to provide guidance for the clinical application of MRI-guided carbon ion radiotherapy. In this study, the Monte Carlo method was used to simulate the dose distribution of carbon-ion pencil beams with different energies under different magnetic fields. We found that the transverse uniform magnetic fields had little effect on the range shortening of the carbon-ion pencil beams, but had obvious impact on the lateral shift, especially at the Bragg peak of the carbon-ion beams. The lateral shift was related to the carbon-ion beam energy and magnetic field strength. According to the simulation results, we obtained an equation for calculating the lateral shift of carbon-ion beams under the magnetic fields, and proposed an angle correction method to reposition the Bragg peak of carbon-ion beams. These results will be used to MRI-guided carbon ion radiotherapy in the future.