PET imaging for the quantification of biologically heterogeneous tumours: measuring the effect of relative position on image-based quantification of dose-painting targets
PET imaging for the quantification of biologically heterogeneous tumours: measuring the effect of relative position on image-based quantification of dose-painting targets
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DOI：
10.1088/0031-9155/55/10/001
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发表时间：
2010-05-21
影响因子：
3.5
通讯作者：
Jeraj, Robert
中科院分区：
文献类型：
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作者：
McCall, Keisha C.;Barbee, David L.;Jeraj, Robert
肿瘤的定量成像是定制治疗和适应性患者护理的基础。因此，我们研究了患者定位错误对临床PET/CT系统产生的生物异质性肿瘤图像可重复性的影响。使用商用多层PET/CT系统获取悬浮在水介质中的含有已知体积和已知放射性浓度的多个球体的幻影的2D和3D PET图像。这些球体作为生物异质性亚肿瘤区域的替代品，尺寸为5-15毫米。在图像采集之间，使用机动臂沿径向或轴向以1mm间隔重新定位球体。使用典型的诊断重建技术重建幻像图像，并对这些图像进行分析，以表征和建模对比度恢复中的位置相关变化。还进行了一项模拟研究，以研究患者体位对生物异质性头颈部（HN）肿瘤PET成像再现性的影响。在本次模拟研究中，我们计算了成像时患者相对位置变化所引起的图像强度值的变化。两名HN患者的PET图像被用来模拟一项影像学研究，该研究纳入了HN患者典型的设置错误。研究人员调查了每位患者的1000个随机定位错误。作为幻像研究的结果，一个位置依赖的趋势被确定为测量小物体的对比度恢复。峰值对比度恢复发生在与图像体素中心重合的径向和轴向位置。相反，当物体位于图像体素的边缘时，对比度恢复最小。将高对比度球的位置改变一半的体素维度，会导致对比度恢复值的测量误差大于30%。然而，发现误差的大小取决于球体的大小和图像重建的方法。对直径为5 mm的球体，标准OSEM图像的误差值为20 ~ 35%，对直径为10 mm的球体，误差值为5 ~ 10%。对比恢复的位置依赖性变化可导致异质性肿瘤图像内空间分布的变化。在模拟两名HN患者成像过程中的随机设置误差的实验中，这些肿瘤的相关性期望值类似于1.0；但Pearson相关系数低至0.8。此外，图像内的变化可以极大地改变生物靶体积的描绘。靶区描绘的错误在异质性很强的肿瘤中更为突出。例如，在相关性为0.8的一对图像中，在最大suv的50% （ROI(50%)）处划定的剂量喷涂目标的体积变化了36%。这些研究结果表明，PET图像中示踪剂的对比度恢复和空间分布容易受到成像时患者/肿瘤位置变化的影响。因此，HN患者的随机设置错误可能导致同一肿瘤的后续图像研究之间的相关性降低。
Quantitative imaging of tumours represents the foundation of customized therapies and adaptive patient care. As such, we have investigated the effect of patient positioning errors on the reproducibility of images of biologically heterogeneous tumours generated by a clinical PET/CT system. A commercial multi-slice PET/CT system was used to acquire 2D and 3D PET images of a phantom containing multiple spheres of known volumes and known radioactivity concentrations and suspended in an aqueous medium. The spheres served as surrogates for sub-tumour regions of biological heterogeneities with dimensions of 5-15 mm. Between image acquisitions, a motorized-arm was used to reposition the spheres in 1 mm intervals along either the radial or the axial direction. Images of the phantom were reconstructed using typical diagnostic reconstruction techniques, and these images were analysed to characterize and model the position-dependent changes in contrast recovery. A simulation study was also conducted to investigate the effect of patient position on the reproducibility of PET imaging of biologically heterogeneous head and neck (HN) tumours. For this simulation study, we calculated the changes in image intensity values that would occur with changes in the relative position of the patients at the time of imaging. PET images of two HN patients were used to simulate an imaging study that incorporated set-up errors that are typical for HN patients. One thousand randomized positioning errors were investigated for each patient. As a result of the phantom study, a position-dependent trend was identified for measurements of contrast recovery of small objects. The peak contrast recovery occurred at radial and axial positions that coincide with the centre of the image voxel. Conversely, the minimum contrast recovery occurred when the object was positioned at the edges of the image voxel. Changing the position of high contrast spheres by one-half the voxel dimension lead to errors in the measurement of contrast recovery values which were larger than 30%. However, the magnitudes of the errors were found to depend on the size of the sphere and method of image reconstruction. The error values from standard OSEM images of the 5 mm diameter sphere were 20-35%, and for the 10 mm diameter sphere were 5-10%. The position-dependent variation of contrast recovery can result in changes in spatial distribution within images of heterogeneous tumours. In experiments simulating random set-up errors during imaging of two HN patients, the expectation value of the correlation was similar to 1.0 for these tumours; however, Pearson correlation coefficient values as low as 0.8 were observed. Moreover, variations within the images can drastically change the delineation of biological target volumes. The errors in target delineation were more prominent in very heterogeneous tumours. As an example, in a pair of images with a correlation of 0.8, there was a 36% change in the volume of the dose-painting target delineated at 50%-of-max-SUV (ROI(50%)). The results of these studies indicate that the contrast recovery and spatial distributions of tracer within PET images are susceptible to changes in the position of the patient/tumour at the time of imaging. As such, random set-up errors in HN patients can result in reduced correlation between subsequent image-studies of the same tumour.