模拟呼吸运动对SBRT剂量分布的影响研究

Effect research of simulated respiratory movement on dose distribution of SBRT

目的研究模拟呼吸运动对不同单次大剂量体部立体定向放疗(SBRT)剂量分布的影响。方法选取2018年1~6月来武汉大学人民医院肿瘤中心治疗的20例肿瘤最大径5 cm的肺癌SBRT患者,每例肺癌都设计七野三维适形和调强适形两组计划,分别对单次剂量为200、400、600、800、1000 cGy进行研究。将美国Sunnuclear公司生产二维半导体阵列Mapchecker置于运动平板上,使用近似运动周期T为3.5 s,跟常人呼吸运动周期相似,运动幅度为±5、±10、±15 mm;比较模拟呼吸运动和静止状态下治疗计划系统输出的相应等中心处水平面剂量分布和实测的剂量分布差异,两组间数据行配对t检验。结果不同运动幅度和不同单次剂量的SBRT三维适形与调强适形计划放疗剂量分布γ分析通过率(3%/3 mm)比较,差异有高度统计学意义(P < 0.01)。结论呼吸运动会导致肿瘤靶区剂量的适形度降低,导致放射剂量分布更加模糊;通过Mapchecker系统软件很容易分析出呼吸运动对3DCRT剂量分布的影响主要集中在靶区头脚方向,可对IMRT的影响分布于整个靶区;同一运动幅度随单次剂量的提高,调强放疗的剂量分布通过率反而比三维适形高。

Objective To study effect of simulated respiratory movement on dose distribution of different single dose stereotactic body radiotherapy (SBRT). Methods Twenty patients with SBRT of lung cancer with a maximum diameter of 5 cm were selected from the Cancer Center in People′s Hospital of Wuhan University from January to June 2018. Seven-field three-dimensional conformal and intensity-modulated conformal plans were designed for each lung cancer patient. The single dose of 200, 400, 600, 800, 1000 cGy was studied respectively. A two-dimensional semiconductor array Mapchecker produced by Sunnuclear Company in the United States was placed on a moving plate. The approximate motion period T was 3.5 s, which was similar to the normal breathing cycle. The range of motion was ±5,±10,±15 mm. Horizontal dose distribution at the corresponding isocentric output of the treatment planning system under simulated respiratory motion and static state and the difference between the measured dose distribution and the measured dose distribution were compared. Results There were significant differences in three-dimensional conformal and intensity-modulated conformal radiotherapy (3%/3 mm) pass rates between SBRT with different movement ranges and different single dose (P < 0.01). Conclusion Respiratory movement can reduce the conformity of dose in tumor target area and make the dose distribution blurred. It is easy to analyze the effect of respiratory movement on dose distribution of 3DCRT by Mapchecker system software, which mainly concentrates on the head and foot direction of target area, and can affect IMRT in the whole target area. The same range of motion is distributed with single dose. The dose distribution of IMRT is higher than that of three dimensional conformation.