小野下光子特征线混合笔束模型肺部剂量算法

为了准确计算小射野下肺模体中精确的三维剂量分布，本文提出了光子特征线混合笔束模型.该模型首先采用光子特征线算法获得参考射野下肺模体的中心轴深度剂量，然后在此基础上对肺模体笔束核进行等效深度修正和加权密度修正.本文利用该算法计算了6 MV光子束在不同射野下不同肺模体的中心轴深度剂量分布，并与蒙特卡罗模拟结果相比较以验证其精度.结果表明，两种方法计算得到的剂量基本一致，大多数深度处的相对误差小于3%.主要差异表现在介质交界处及肺组织前部，其相对误差随着射野尺寸和肺密度的增大而减小，最大相对误差范围为7.8%～36.9%.在肺组织前部，相对误差大于3%的深度范围随射野尺寸的增大和肺密度的减小而增大.因此，该算法在小射野下的肺部剂量计算中具有潜在的研究价值.

Photon characteristic line hybrid pencil beam model for lung phantoms under condition of small fields

In order to accurately calculate the three-dimensional dose distribution in a lung phantom photon under a small fied, photon characteristic line hybrid pencil beam model has been proposed. The model is based on the photon characteristic line algorithm to obtain the depth dose for lung phantoms in the reference field. On this basis, the pencil beam kernel of lung phantom is processed by heterogeneous correction, including equivalent depth correction and weighted density correction. Finally, the pencil beam kernel for lung phantom is calculated for obtaining the dose at each point on the central axis for the 6 MV photon beam. The results show that the central axis percentage depth dose obtained by this algorithm is basically consistent with the Monte Carlo simulation results, and the relative error is less than 3% in most cases. Especially in the middle and posterior portion of lung, the average relative error is less than 1%. However, the dose difference between the two methods is obvious at media interfaces and lung anterior portion, and the relative errors decrease with the increase of field size and lung density, with the maximum relative error ranging from 7.8% to 36.9%. Nevertheless, the model can accurately describe the dose distribution in small fields for lung radiotherapy.