椎体转移瘤立体定向放射治疗剂量跌落梯度分析

摘要

目的：分析评价利用Cyberknife系统实施立体定向放射治疗(SBRT)技术治疗椎体转移瘤时，脊髓方向的剂量跌落趋势。方法：利用Cyberknife治疗8例胸椎转移瘤患者，根据放射治疗剂量的不同将其分为两组，其中4例患者给予靶区剂量40 Gy/5次(40 Gy组)；4例患者给予靶区剂量33 Gy/3次(33 Gy组)。采用Cyberknife系统自带的MultiPlan4.0.2治疗计划系统设计优化治疗计划，针对靶区处方剂量跌落梯度、相对剂量跌落梯度以及单位距离剂量跌落梯度3方面。统计分析Cyberknife系统治疗计划中在脊髓方向的剂量跌落趋势。结果：40 Gy组单位绝对剂量跌落速度为(0.208±0.085)mm/100 cGy，相对剂量跌落为(0.87±0.60)mm/5%Dmax，单位距离跌落速度为(353.63±160.48) cGy/mm。33 Gy组单位绝对剂量跌落速度为(0.311±0.089)mm/100 cGy，相对剂量跌落为(0.69±0.16)mm/5%Dmax，单位距离跌落速度为(266.27±94.41)cGy/mm。40 Gy组优于33 Gy组。结论：Cyberknife系统治疗椎体转移瘤时脊髓方向剂量跌落极快，对脊髓保护好；将Cyberknife精确的追踪系统应用于椎体转移瘤的立体定向放疗，对脊髓的保护安全有效。%Objective:To evaluate the dose falling gradient in the direction of the spinal cord while implementing SBRT (Stereotactic Body Radiation Therapy) technology by Cyberknife in the treatment of spinal metastases.Methods: Eight patients with spinal metastases treated with SBRT by Cyberknife were selected. Two different RT schedules were administered, 40Gy per 5 fractions(n=4), The other was 33Gy per 3 fractions(n=4). We ues the MultiPlan4.0.2 treatment planning system owning by Cyberknife system design and optimize the treatment plan. We have analysis of the dose falling gradient, speed and the falling capacity of Cyberknife treatment plan in three aspects, such as the target prescription dose falling gradient, relative dose falling gradient, and the dose falling gradient of unit distance in the direction of spinal cord.Results: For the group of 40Gy, absolute dose falling speed can be(0.208±0.085)mm/100cGy,relative dose falling is (0.87±0.60)mm/5%Dmax, the falling of unit distance can reach (353.63±160.48)cGy/mm. Similarly, for the other group of 33Gy, absolute dose falling speed is (0.311±0.089)mm/100cGy, relative dose falling is(0.69±0.16)mm/5%Dmax, the falling gradient of unit distance can be 266.27±94.41cGy/mm. The group of 40Gy seems to be better than that of 33Gy group.Conclusion: The dose in the direction of spinal cord fall fast in the treatment of spinal metastases by Cyberknife, providing a perfect protect to the spinal cord. With the addition of its unique and precise target tracking system, the using of Cyberknife in spinal metastases of SBRT for the protection of the spinal cord is safe and effective.