Changes of three-dimensional reconstruction for the tumor targets in radiotherapy

Abstract

AIM：To investigate the effect of respiration on the three-dimensional reconstruction of the tumor targets in lung.

METHODS：The phantom, which simulated the respiration, was made by step motor, motor driver, reactor, small ball of polymethyl methacrylate and low-density foam. Six series with different scan pitches (0.875, 1.675, 0.625 mm), slice thickness (8 mm×1.25 mm or 8 mm×2.50 mm), periods and initial phases were set, and the phantom was scanned using GE LightSpeed16 CT scanner. The three-dimensional reconstruction of CT images of the phantom was completed by adopting the volume rendering technology, and the volumes of each target in different series were measured by the three-dimensional measuring tools. Thus, the changing scale of motional targets compared with the stationary ones were calculated.

RESULT: There was no obvious difference in the three-dimensional reconstructions of stationary targets, which were scanned with different pitches and slices. There were marked differences in the three-dimensional reconstructions of different motional targets, and the maximal change of volume relative deviation was 54.1% for the same target scanned with different pitches, slices and periods. The change scale of reconstruction volume was variable among the different targets, it was －39.8% to 54.1% for the smaller targets and －18.4% to 8.7% for the larger targets.

CONCLUSION:The respiration has great effects on the three-dimensional reconstruction of the tumor targets. The CT images adopted in three-dimensional treatment planning system must be the stationary images. Otherwise, the conformal radiation fields will be distorted greatly and the dose-volume histogram will be false.

Xu ZH, Liao FX, Zhou YH, Huang J, Zhou ZM.Changes of three-dimensional reconstruction for the tumor targets in radiotherapy.Zhongguo Zuzhi Gongcheng Yanjiu yu Linchuang Kangfu 2007;11(13):2487-2489,2493(China)
[www.zglckf.com/zglckf/ejournal/upfiles/07-13/13k-2487(ps).pdf]

摘要
目的：观察呼吸运动对肺部靶区三维重建的影响。
方法：用步进电机、步进电机驱动器、导轮、有机玻璃球、低密度度泡沫等设计能模拟肿瘤随呼吸运动的体模；取不同螺距（0.875，1.675，0.625 mm）、不同层厚（8 mm×1.25 mm或8 mm×2.50 mm）和运动周期组成6个不同的扫描序列在GE LightSpeed 16 CT上扫描，然后采用体绘制技术对所获得CT图像进行三维重建，用三维工具软件测量不同扫描条件下各靶体积大小，计算动态与静态扫描靶区重建体积的相对偏差。
结果：静态模型同一靶区在层厚与螺距不同时，扫描后三维重建的靶区外形无明显变化，重建靶区的体积差异可忽略；在不同运动状态下扫描，同一靶区重建图像的外形差异明显，重建靶体积的相对偏差最大值为54.1%；同一运动状态下，各靶区重建体积变化随靶而异；外形较小的靶区重建体积相对偏差变化范围为－39.8%~54.1%，外形较大的靶区重建体积相对偏差变化范围是－18.4%~8.7%。
结论：呼吸运动对靶区重建的响影极大，三维放疗计划设计所依赖的CT图像，必须是肿瘤靶区处于相对静止状态下扫描的图像，否则，适形射野和剂量体积直方图将严重失真。
关键词：呼吸运动；模型；三维重建；康复工程

徐子海，廖福锡，周燕华，黄坚，周志美.运动状态下CT扫描后靶区三维重建的形变规律[J].中国组织工程研究与临床康复，2007，11(13):2487-2489,2493 [www.zglckf.com/zglckf/ejournal/upfiles/07-13/13k-2487(ps).pdf]