周期运动靶区受照剂量分布的模拟计算及验证

Simulation and verification of dose distribution of cycle motion target

目的基于剂量矩阵叠加算法计算周期运动靶区的剂量分布，并验证其准确性。方法用二维空气电离室矩阵MatriXX系统和周期运动平台相配合，实测靶区在静态和周期运动状态下进行调强放疗时的剂量分布。根据周期运动靶区在照射过程中的运动特点，提出了预测其剂量分布的剂量矩阵叠加算法，并用Matlab 7．0工具软件编写了相应的模拟计算程序，预测了不同运动幅度（±5、±10、±15mm）时靶区的剂量分布。结果周期运动靶区的模拟剂量分布与静态靶区的实测剂量分布相比，在靶区中心大部分区域二者相对偏差小于1％，在靶区运动方向，模拟的高剂量区域向内收缩，低剂量区域向外扩张，但50％等剂量曲线范围未见明显改变。周期运动靶区的模拟剂量分布与动态下的实测分布相比，二者的离轴比几乎重合，仅在射野外的低剂量区域中（〈10％）有细微偏差。结论剂量矩阵叠加算法能较准确计算周期运动靶区的受照剂量分布。

Objective To simulate the dose distribution of the cycle motion target based on the dose matrix superposing method, and to verify the dose distribution. Methods A 2D air vented ionization chamber array MatriXX system and a cycle motion platform were used to measure 2D dose distribution of static and cycle motion target irradiated by IMRT segment beams. According to the features of the cycle motion target, a dose matrix superposing method was put forward, and the corresponding simulation program was developed by applying Matlab 7.0 software tools. The dose distributions of cycle motion target with different amplitudes （ _＋5, ＋ 10, _＋ 15mm） were calculated through the simulation program. Results The deviation between the measured dose of static target and the calculated dose of cycle motion target was less than 1% at the central area. Compared with the measured dose distribution of static target, the calculated high dose area of the motion target was shrunk inward and the low dose area was extended outward, but the area of 50% isodose changed insignificantly. The calculated and measured off-axis ratios （OAR） of the cycle motion target were almost identical at motion direction. There was only imperceptible deviation in the low dose area （less than 10% ） out of field. Conclusions The dose matrix superposing method can be applied to precisely calculate the dose distribution of cycle motion target.