Quantitative assessment of the physical potential of proton beam range verification with PET/CT
Quantitative assessment of the physical potential of proton beam range verification with PET/CT
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DOI：
10.1088/0031-9155/53/15/009
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发表时间：
2008-08-07
影响因子：
3.5
通讯作者：
Bortfeld, T.
中科院分区：
文献类型：
--
作者：
Knopf, A.;Parodi, K.;Bortfeld, T.
最近的一项临床试点研究证明了质子治疗中离线PET/CT范围验证的可行性。活体PET测量受到血液灌流、组织成分变化、患者运动和图像联合配准不确定性的挑战。除了这些生物和治疗特有的因素外，该方法的准确性还受到潜在物理过程的限制。这项体模研究将物理因素与其他因素区分开来，评估PET/CT范围验证方法的重复性、一致性和灵敏度。向由聚甲基丙烯酸甲酯(PMMA)、肺和骨等效材料板组成的体模提供了扩展的布拉格峰(SOBP)质子场。在距质子治疗单元步行10分钟内可买到的商用PET/CT扫描仪上，以列表模式获取PET数据。将测量的PET活性分布与基于Geant4和FLUKA蒙特卡罗(MC)程序的PET信号模拟进行了比较。为了测试测量的PET信号的重复性，比较了体模中相同几何位置的两个独立测量的数据。此外，还比较了相同材料排列但在照射场内不同位置的激活深度分布，以检验测量的PET信号的一致性。最后，研究了空气/肺、空气/骨和肺/骨界面以及与射束方向平行的6个方向的激活深度分布，以考察PET/CT距离验证方法的敏感性。测量的PET信号的重复性和一致性被发现是相同的数量级。他们确定PET测量的物理精度约为1毫米。然而，在PET扫描仪的光束边缘和视野(FOV)边缘，发现两次测量之间的距离差异高达2.6 mm，以及一次测量内的范围变化高达2.6 mm。PET/CT范围验证被发现能够在存在复杂的组织不均匀的情况下检测到小范围的改变。这项研究表明，PET/CT验证方法在检测患者体内递送剂量的全程特性方面具有物理潜力。
A recent clinical pilot study demonstrated the feasibility of offline PET/CT range verification for proton therapy treatments. In vivo PET measurements are challenged by blood perfusion, variations of tissue compositions, patient motion and image co-registration uncertainties. Besides these biological and treatment specific factors, the accuracy of the method is constrained by the underlying physical processes. This phantom study distinguishes physical factors from other factors, assessing the reproducibility, consistency and sensitivity of the PET/CT range verification method. A spread-out Bragg-peak (SOBP) proton field was delivered to a phantom consisting of poly-methyl methacrylate (PMMA), lung and bone equivalent material slabs. PET data were acquired in listmode at a commercial PET/CT scanner available within 10 min walking distance from the proton therapy unit. The measured PET activity distributions were compared to simulations of the PET signal based on Geant4 and FLUKA Monte Carlo (MC) codes. To test the reproducibility of the measured PET signal, data from two independent measurements at the same geometrical position in the phantom were compared. Furthermore, activation depth profiles within identical material arrangements but at different positions within the irradiation field were compared to test the consistency of the measured PET signal. Finally, activation depth profiles through air/lung, air/bone and lung/bone interfaces parallel as well as at 6. to the beam direction were studied to investigate the sensitivity of the PET/CT range verification method. The reproducibility and the consistency of the measured PET signal were found to be of the same order of magnitude. They determine the physical accuracy of the PET measurement to be about 1 mm. However, range discrepancies up to 2.6 mm between two measurements and range variations up to 2.6 mm within one measurement were found at the beam edge and at the edge of the field of view (FOV) of the PET scanner. PET/CT range verification was found to be able to detect small range modifications in the presence of complex tissue inhomogeneities. This study indicates the physical potential of the PET/CT verification method to detect the full-range characteristic of the delivered dose in the patient.