不同CT模拟定位条件对射波刀图像引导头部体位系统误差的影响研究
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摘要
目的:研究头颅模体在不同CT扫描条件下模拟定位图像对射波刀(CK)G4系统六维颅骨追踪(6D-skull)技术相同图像引导条件下头部体位系统误差的影响。方法:使用头颅模体(Lucy)模拟患者,将CT的X射线管不同管电压分为80 k V组、100 k V组、120 k V组及140 k V组,在不同管电压、相同管电流(440 m As)下,模体相同扫描层厚1 mm,分别获取CT模拟定位(CT-sim)图像。通过Multi Plan计划系统分别生成相应的两幅正交定位数字重建图像(DRR)。将头颅模体置于治疗床面,按照CT-sim中心点摆位,采用CK图像引导系统的两个正交X射线管同时曝光与分别曝光方式,且曝光参数相同,记录每组、每种曝光方式各采集100份的3个线性方向(X轴、Y轴和Z轴)和3个旋转方向(L-R旋转、UP-DOWN旋转和CW-CCW旋转)6个方向的体位误差数据。根据公式M=2.5∑+0.7δ计算X轴、Y轴和Z轴3个线性方向的外扩边界。结果:每种图像引导曝光方式相同方向头部体位误差数据各组之间差异均有统计学意义(F=39.133,F=235.431,F=234.349,F=31.638,F=289.814,F=515.825;P<0.01)。两种曝光方式不同管电压组头部体位误差数据以120 kV组头部体位误差绝对值数据分析中的标准差较小,头部体位误差较稳定。计算两种曝光方式,不同管电压条件下3个线性方向中各类头部体位误差数据外放范围最大值为0.402 mm,最小值为0.009 mm,95%置信区间(95%CI)为0.17～0.27 mm。结论:CT不同X射线管电压条件模拟定位图像,对相同条件图像引导产生的头部体位系统误差是有一定影响。在电压120 k V,440 m As下的模拟定位图像对CK-G4系统图像引导放射治疗(IGRT)头部体位系统误差影响较小、系统误差的稳定性好,可提高CK-G4系统立体定向放射治疗图像引导的精准度。
Objective: To study the influence of the simulated positioning image of skull phantom under different CT scan conditions on the system error of head position under guided condition of same image with six dimensional-skull tracking(6D-skull) technique of the CyberKnife(CK) G4 system. Methods: The skull phantom(Lucy) was used to simulate patient, and the X-ray tubes of CT were divided into 80 kV group, 100 kV group, 120 kV group and 140 kV group. Under the different tube voltage and same tube current(440 mAs), the thickness of same scanning layer of phantom was 1mm, and the CT simulation positioning(CT-sim) imagines were respectively obtained. And the corresponding two digital reconstructed radiographs(DRR) with orthogonal position were generated through the MultiPlan planning system. The skull phantom was putted on the treatment bed, and was positioned as CT-sim center point. And the simultaneous exposure and respective exposure of two orthogonal X-ray tubes of guidance system with CK image were adopted and their exposure parameters were same. The 100 position error data of six directions, that included three linear directions(X-axis, Y-axis and Z-axis) and three rotation directions(L-R rotation, UP-DOWN rotation and CW-CCW rotation), of each group and each exposure mode were recorded, respectively. And then the boundary of external expansion of three linear directions were calculated as the formula: M=2.5∑+0.7δ. Results: The differences of head position error data at the same direction of exposure mode under the guidance of each image among different groups were significant(F=39. 133, F=235.431, F=234.349, F=31.638, F=289.814, F=515.825, P<0.01). In these head position error data of different tube voltage of two kinds of exposure modes, the standard deviation of absolute value of head position error of 120 kV group was lesser, and the head position error was more stable. The maximum value of external expansion range of different kinds of head position error data at three linear directions under different tube voltage was 0.402 mm, and the minimum value was 0.009 mm, and 95% confidence interval(95% CI) was from 0.17 to 0.27 mm. Conclusion: The position image that is simulated by different X-ray tube voltage of CT has a certain influence on the head position system error that is generated by the guidance with same condition image. And the simulated location image under the 120 kV and 440 mAs has smaller influence on the head position system error of image guided radiotherapy(IGRT) of CK-G4 system, and the stability of system error is better, and can increase the precision and accuracy of image guidance of stereotactic radiotherapy of CK-G4 system.
Objective: To study the influence of the simulated positioning image of skull phantom under different CT scan conditions on the system error of head position under guided condition of same image with six dimensional-skull tracking(6D-skull) technique of the CyberKnife(CK) G4 system. Methods: The skull phantom(Lucy) was used to simulate patient, and the X-ray tubes of CT were divided into 80 kV group, 100 kV group, 120 kV group and 140 kV group. Under the different tube voltage and same tube current(440 mAs), the thickness of same scanning layer of phantom was 1mm, and the CT simulation positioning(CT-sim) imagines were respectively obtained. And the corresponding two digital reconstructed radiographs(DRR) with orthogonal position were generated through the MultiPlan planning system. The skull phantom was putted on the treatment bed, and was positioned as CT-sim center point. And the simultaneous exposure and respective exposure of two orthogonal X-ray tubes of guidance system with CK image were adopted and their exposure parameters were same. The 100 position error data of six directions, that included three linear directions(X-axis, Y-axis and Z-axis) and three rotation directions(L-R rotation, UP-DOWN rotation and CW-CCW rotation), of each group and each exposure mode were recorded, respectively. And then the boundary of external expansion of three linear directions were calculated as the formula: M=2.5∑+0.7δ. Results: The differences of head position error data at the same direction of exposure mode under the guidance of each image among different groups were significant(F=39. 133, F=235.431, F=234.349, F=31.638, F=289.814, F=515.825, P<0.01). In these head position error data of different tube voltage of two kinds of exposure modes, the standard deviation of absolute value of head position error of 120 kV group was lesser, and the head position error was more stable. The maximum value of external expansion range of different kinds of head position error data at three linear directions under different tube voltage was 0.402 mm, and the minimum value was 0.009 mm, and 95% confidence interval(95% CI) was from 0.17 to 0.27 mm. Conclusion: The position image that is simulated by different X-ray tube voltage of CT has a certain influence on the head position system error that is generated by the guidance with same condition image. And the simulated location image under the 120 kV and 440 mAs has smaller influence on the head position system error of image guided radiotherapy(IGRT) of CK-G4 system, and the stability of system error is better, and can increase the precision and accuracy of image guidance of stereotactic radiotherapy of CK-G4 system.
引文
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[2]宫照利,凌华浓,林英金,等.CT机建设与质量控制[J].中国医学装备,2011,8(7):50-53.
[3]李锋坦,李东,张云亭.管电压对CT值测量、辐射剂量及图像质量影响的模型研究[J].中华放射学杂志,2013,47(5):458-461.
[4]彭文献,彭天舟,叶小琴,等.CT扫描参数对人体组织CT值影响的研究[J].中华放射医学与防护杂志,2010,30(1):79-81.
[5]牛保龙,鞠忠建,戴相昆,等.六维颅骨追踪技术在头部肿瘤放射治疗过程中体位误差的研究[J].中国医学装备,2017,14(3):33-35.
[6]van Herk M,Remeijer P,Rasch C,et al.The probability of correct target dosage:dosepopulation histograms for deriving treatment margins in radiotherapy[J].Int J Radiat Oncol Biol Phys,2000,47(4):1121-1135.
[7]van Herk M.Errors and margins in radiotherapy[J].Semin Radiat Oncol,2004,14(1):52-64.
[8]Das IJ,Cheng CW,cao M,et al.Computed t o m o g r a p h y i m a g i n g p a r a m e t e r s f o r inhomogeneity correction in radiation treatment planning[J].J Med Phys,2016,41(1):3-11.
[9]Zurl B,Tiefling R,Winkler P,et al.Hounsfield units variations:impact on CT-density based conversion tables and their effects on dose distribution[J].Strahlenther Onkol,2014,190(1):88-93.
[10]廖雄飞,黎杰,王培.CT模拟定位机的扫描参数对放疗计划系统剂量计算的影响[J].肿瘤预防与治疗,2015,28(1):49-51.
[11]Nithiananthan S,Schafer S,Uneri A,et al.Demons deformable registration of CT and conebeam CT using an iterative intensity matching approach[J].Med Phys,2011,38(4):1785-1798.
[12]Nithiananthan S,Brock KK,Daly MJ,et al.Demons deformable registration for CBCT guided procedures in the head and neck:Convergence and accuracy[J].Medical Physics,2009,36(10):4755-4764.
[13]Boschini FJ,Commander CW,Schreiber EC,et al.Comparison of gold seeds,tight embolization coils,and loose embolization coils used as fiducial markers for dynamic tracking using CyberKnife[J].Pract Radiat Oncol,2013,3(2 Suppl 1):S22.