螺旋CT用于确定运动靶区时的体积重建缺陷的模体研究

A phantom study for the reconstruction defects of moving target volume decision by spiral CT

目的 用已知体积模体按放疗需要常规CT扫描,比较螺旋CT在图像三维重建时的体积与真实体积之间差异.方法 以呼吸运动模拟装置为基础,采用蜡块制作成不同体积的规则模体1～9个,设置运动幅度为2.5 cm,运动频率为18次/min.将9个模体同时不连续扫描10次,计算螺旋CT对不同已知静止、运动物体三维重建时体积与真实体积之间差异并行配对t检验.结果 所有模块合计的三维重建体积大于其已知静止体积（121.77 cm^3：103.14 cm^3,P=0.038）,但又明显小于其已知运动体积（121.77 cm^3：161.75 cm^3,P =0.045）,这种现象在不同体积模块的体积重建过程中得到了重复.不同体积模块重建体积与已知运动、静止体积的相对偏差均呈现随模块体积变小而增大的趋势.结论 对运动靶区而言,由于螺旋CT扫描速度很快使扫描过程中存在着重复扫描和漏扫情况,导致所获靶体积不能完整代表ITV.

Objective To investigate reasonable method of deciding internal target volume （ITV） by comparing physical phantom volumes （including moving volume） with reconstruction volumes of spiral CT scanning.Methods The various-volume wax blocks which were labeled No.1-9 were made and put on the respiratory motion simulator.The range of motion was set 2.5 cm and frequency 18 beats/min.All blocks were scanned 10 times continuously and imported into the Eclipse TPS.All blocks volumes were calculated and then compared with the true physical volumes and paired t-test.Results The reconstruction volumes of 1-9 blocks were bigger than their stationary volumes （121.77 cm^3 vs.103.14 cm^3,P =0.038）,but significantly smaller than their moving volumes （121.77 cm^3 vs.161.75 cm^3,P =0.045）.The results can be gotten in different volume block scanning.The relative deviation of reconstruction volumes and the moving volumes tends to increase as the stationary physical volume decreases.Conclusions As to moving targets,conventional spiral CT scanning speed is too fast to collect all volume information of targets.So the one-time-scanning volume does not represent the ITV.