基于MatriXX系统研究呼吸运动对靶区受照剂量分布影响

目的 探讨呼吸运动对三维适形放疗(3DCRT)和调强放疗(IMRT)靶区受照剂量分布影响.方法 用固体水自制剂量测量体模和模拟呼吸运动的平台,与二维空气电离室矩阵MamXX系统配合,分别测量体模在静态和周期运动状态(幅度为±1 cm,周期3.5 s)下进行多角度3DCRT和IMRT的二维剂量分布,然后用MatriXX系统软件对两种不同状态下所测剂量分布进行对比分析.结果 对3DCRT在运动方向上所测剂量分布半影较静态时增加6～9 mm,高剂量区域向内收缩约5mm,低剂量区域向外扩张约5 mm,但50%等剂量曲线范围及中心区域剂量未见明显改变;IMRT各子野单独照射且以测量平面最大剂量为归一剂量时,运动和静止状态下所测剂量差异介于-56.4%～56.1%,其平均值约±27%;IMRT计划所有子野叠加照射时,两种运动状态下在射野中绝大部分区域的剂量差异<±3%,其剂量偏差主要出现在射野边缘,最大约为±15%,这与3DCRT照射的特点相似.结论 无论是3DCRT还是IMRT多次分割照射后,周期运动靶区中心区域受照剂量与静态靶区相近,但高剂量区域向内收缩,低剂量区域向外扩张.

MatriXX system in the study of the influence of respiratory motion on target dose distribution

Objective To investigate the influence of respiratory motion on target dose distribution in three-dimensional conformal radiation therapy(3DCRT) and intensity modulated radiation therapy(IM-RT). Methods A 2D air vented ionization chamber array MatriXX system,a platform which can mimic the clip motion of lung tumor, and a home-made solid water(RW3) phantom were used to measure the 2D dose distribution of static and moving targets irradiated by 3DCRT and IMRT beams using multiple gantry an-gles. The period of the moving platform was set to 3.5 s and the amplitude was ± 1 cm. Then the differences of dose distribution between the static phantom and moving phantom were compared and analyzed with the MatriXX system software. Results Compared with the static phantom in 3DCRT, the penumbra of dose distribution of the periodic moving phantom along the moving directions was increased by 6-9 mm, the high dose area was shrinked by about 5 ram,and the low dose area was extended by 5 mm,but the area of 50% i-sodose and the dose center area changed very little. When a single segment beam of IMRT was delivered and measured and the maximum dose of measuring plane was normalized to 100% ,the average difference of dose distribution between the static and dynamic phantoms was ±27% (from -56.4% to 56.1%) ;When all of the segment beams of IMRT were dehvered and the integrated dose distribution was measured ,the dose differ-ences were less than ±3% ,and the maximum difference of dose distribution was about ±15% which mainly appeared at the field margin and were similar to 3DCRT. Conclusions The dose distribution of most cen-ter areas of the periodic moving target using multi-fraction 3DCRT/IMRT beams is similar to that of the static target, while the high dose area of the former is shrinked and the low dose area is extended.