基于4D-CT研究随呼吸运动靶区的剂量分布规律

目的:基于4D-CT探讨随呼吸运动靶区的受照剂量分布特征及进行个体化精确放疗计划设计方法。材料和方法:患者在自由呼吸状态下进行多床位Cine模式扫描,每个床位Cine扫描持续时间约4s～6s。扫描后,用研究开发的4D-CT图像重建系统对所得图像进行4D-CT、最大密度投影(MIP)和平均密度投影(AIP)重建,生成多相位4D-CT、MIP和AIPCT。将重建图像传入放疗计划系统中,分别以呼气末相4D-CT、AIPCT和MIPCT图像作为基准图像,其它相位4D-CT作为融合图像进行图像配准,在基准图像上勾画靶区并进行放疗计划设计,比较基准图像和融合图像中靶区的剂量分布。结果:当肿瘤靶区位于肺尖时,呼气末相和吸气末相4D-CT中靶区的剂量分布无明显差异;靶区在肺中部和腹部时,在呼气末相4D-CT上设计的放疗计划,其剂量分布不能很好地覆盖吸气末相时的靶区,可能导致靶区漏照射;在MIP和AIPCT上设计的放疗计划,其剂量分布能较好地覆盖呼气末相/吸气末相时的靶区。结论:基于4D-CT能直观地得到不同呼吸相位时靶区的剂量分布,利用MIP和AIPCT可快速实现运动靶区的个体化精确放疗计划设计。

Research about the Dose Distribution of Moving Targets Based on 4D-CT Image

Objective： To study the dose distribution characteristics and individualized precise radiotherapy planning method based on 4D-CT images in the presence of respiration-indnced organ motion. Methods：CT data of patients were acquired under free breathing state in axial cine mode for multiple couch positions. The scanner continuously acquired projection data of patients at each couch position for 4.0 s-6.0 s. A 4D-CT reconstruction system developed in house was used to reconstruct 4D-CT, maximum intensity projection （MIP） CT and average intensity projection （A/P） CT, which were used as the base images or fusion images separately. The target contoures and treatment planning were based on the base images. The dose distribution of targets on base images were compared with that on fused images. Results：When lung tumors were located in the tip, there was no obvious difference of dose distribution in the target area between end-expiratory and end-inspiratory phase 4D-CT images. When the targets were located in the lung and abdominal part, the dose distribution based on the end-expiratory phase 4D-CT couldn＇t entirely cover the targets in end-inspiratory phase. The dose distribution of treatment planning based on AIP/M/P CT could cover the whole target area in end-expiratory and end-inspiration phases. Conclusions： The dose distribution of motion targets in different respiratory phase can be achieved by using 4D-CT images. The individualized precise radiotherapy planning for moving targets can be implemented by using M/P/AIP CT images.