摆位误差对肝癌立体定向放射治疗剂量学的影响

目的:在锥形束CT（CBCT）图像引导下，测量立体定向放射治疗（SBRT）中肝癌的摆位误差，并讨论摆位误差对靶区PTV和危及器官（OAR）剂量的影响。方法:回顾性分析接受SBRT的肝癌患者13例，每日放射治疗前行CBCT扫描，与计划CT图像进行灰度配准，根据肿瘤靶区及OAR位置获取患者移床参数，在计划系统中计算剂量分布，并分析移床参数对靶区PTV、OAR剂量和均匀性指数（HI）、适形度指数（CI）等一系列剂量学参数的影响。结果:校正后X、Y、Z方向上的摆位误差分别为（0.47±2.00）、（1.54±4.16）、（0.10±2.77） mm，Y方向上的摆位误差较大。相对于最小位移，最大位移对靶区、HI和CI影响大；对于OAR，与原始计划相比，左肾、小肠最大位移的剂量分布在Dmean、Dmax上具有统计学意义，右肾最小位移的剂量分布在Dmean上具有统计学意义。结论:≤3 mm的摆位误差对靶区剂量的影响比>5 mm的影响小，但对于最小剂量和覆盖率仍然影响显著。应该尽可能减小摆位误差，以实现精确放疗。

Effects of setup error on the dosimetry of stereotactic body radiotherapy for liver cancer

Abstract: Objective Under the guidance of cone-beam CT (CBCT) images, the setup error of stereotactic body radiotherapy (SBRT) for liver cancer was measured, and the effect of setup error on the PTV and organ-at-risk (OAR) dose in the target area was discussed. Methods 13 liver cancer patients who received SBRT was reviewed retrospectively. CBCT image was taken before each daily radiotherapy and then the gray-scale registration was done with the planning CT images. Based on the coach shifting parameters from the tumor target area and OAR position,the dose distribution in the planning system was calculated, and the effects of coach shifting parameters on a series of dosimetric parameters such as PTV, OAR dose, uniformity index (HI), and conformity index (CI) was analyzed. Results After correction, the setup errors in X, Y and Z directions are (0.47±2.00), (1.54±4.16) and (0.10±2.77) mm respectively, and the setup error is larger in Y direction. Compared with the minimum displacement, the maximum displacement has a significant effect on the target area, HI and CIF. As for OARs, compared with the original plan, the dose distribution of the maximum displacement in the left kidney and small intestine is statistically significant in the Dmean and Dmax, and the dose distribution of the minimum displacement in the right kidney is statistically significant in the Dmean. Conclusion The effect of setup error ≤3 mm on the dose of target area is smaller than that >5 mm, but the effect still has a significant impact on the minimum dose and coverage rate. In order to achieve accurate radiotherapy, the setup error should be minimized as much as possible.