Tomotherapy不同MVCT扫描模式的成像剂量及对儿童患者位置验证精度的影响

目的:探究螺旋断层放疗（Helical TomoTherapy, 以下简称TOMO）高能X线计算机体层摄影术（MVCT）3种扫描模式的成像剂量及其对儿童患者位置验证精度的影响。方法:使用Exradin A1SL电离室测量标准虚拟水模体（Cheese phantom）相同采样点处3种扫描模式的剂量。使用CIRS 1岁婴儿和5岁儿童仿真人模体模拟MVCT引导摆位流程，将“fine”模式引导的床值作为参考，比较其他两种模式的偏差值。结果:“fine”模式下的剂量约为“normal”模式下的2倍（2.003±0.048），“fine”模式下的剂量约为“coarse”模式下的3倍（3.056±0.099），与螺距的比例关系一致。“normal”模式的偏差符合临床容差范围（±1 mm），且结果［等中心点偏差:1岁婴儿:0.53 mm（头颈），0.25 mm（盆）；5岁儿童:0.36 mm（头颈），0.12 mm（盆）］均优于“coarse”模式［等中心点偏差:1岁婴儿:0.59 mm（头颈），0.99 mm（盆）；5岁儿童:1.11 mm（头颈），1.11 mm（盆）］。结论:TOMO MVCT的辐射剂量和位置验证精度与螺距成反比，“coarse”模式尤其是进出方向的引导精度欠佳，需予以特别关注和必要的人工干预。

Imaging doses and positioning accuracy under different scanning modes of Tomotherapy MVCT for pediatric patients

Objective To investigate the imaging doses needed for helical tomotherapy(TOMO)megavoltage computed tomography(MVCT)using 3 scanning modes for pediatric patients and study the effects of different scanning modes on positioning accuracy.Methods Under 3 scanning modes,the imaging dose to the identical sample points in a virtual water phantom(Cheese phantom)were measured using an ExradinA1SL chamber.CIRS 1-year-old infant and 5-year-old pediatric anthropomorphic phantoms were used for stimulating the MVCT-guided positioning.The registration accuracies of"normal"and"coarse"modes were compared with that of"fine"mode.Results The imaging doses of"fine"mode were about 2(2.003±0.048)and 3(3.056±0.099)times higher than those-of"normal"and"coarse"modes,which were consistent with the pitch ratio.The deviations of"normal"mode were within clinical tolerance(±1 mm)and the results were better than those of"coarse"mode.The isocenter deviations of"normal"mode versus"coarse"mode were 0.53 mm vs 0.59 mm(head and neck),0.25 mm vs 0.99 mm(pelvis)for 1-year-old infant phantom,and 0.36 mm vs 1.11 mm(head and neck),0.12 mm vs 1.11 mm(pelvis)for 5-year-old pediatric phantom.Conclusion The imaging dose and positioning accuracy of TOMO MVCT were negatively correlated with the pitch ratio.The accuracy of"coarse"mode was relatively lower especially in longitudinal direction,which requires special attention and manual intervention if necessary.