摘要: 中国科学院近代物理研究所（IMP）目前的重离子治疗计划系统是采用单一高斯模型来描述笔形束的横向剂量分布的，但是对重离子在介质中产生的次级粒子剂量贡献考虑不充分的单一高斯模型不足以描述真实的笔形束横向剂量分布。精确的笔形束模型还应该包含描述由次级粒子所产生的低剂量包络。本研究对笔形束精确模型中对离轴区域低剂量包络的成因、性质、剂量贡献、数学模型及低剂量包络探测方法的研究进展进行了综述，并基于武威重离子治疗中心医用重离子加速器示范装置（HIMM-WW）水平束治疗头的设备布局，利用Monte Carlo方法模拟计算了不同能量重离子笔形束的离轴剂量分布，探讨了模拟计算所得笔形束横向剂量分布与不同数学模型的符合程度。验证了已有文献中所提到的三重高斯模型能更好地描述笔形束的横向剂量分布这一结论。这些工作为下一步改进IMP重离子治疗计划系统中的重离子笔形束模型奠定了基础。


The heavy ion treatment planning system of Institute of Modern Physics(IMP), Chinese Academy of Sciences adopts single Gaussian model to depict the lateral dose distribution of pencil beam currently. Without taking secondary particles produced by heavy-ion pencil beam in medium into full consideration, the single Gaussian model is not accurate enough to describe the lateral dose distribution. In fact, an accurate pencil beam model should include the description of low dose envelope contributed by secondary particles. This work summarized the cause of formation, property, dose contribution, mathematic models and measuring methods of the low dose envelope laterally far away from the incident axis of a pencil beam. Moreover, the lateral dose distribution of heavy ion pencil beams with different energies were calculated by means of the Monte Carlo simulation method, based on the horizontal nozzle of the demonstration facility of heavy ion medical machine in the Wuwei heavy-ion therapy center, and thus the degree of coincidence between the simulated data and different mathematic models was investigated. The results verified that the triple Gaussian model was better than the single and double Gaussian models to depict the lateral dose distribution of heavy ion pencil beams, mentioned from existing papers. Thus, this work provides a basis for further developing practical and accurate pencil beam model for heavy ion cancer therapy.