Knopf A, Parodi K, Paganetti H, Cascio E, Bonab A, Bortfeld T
Department of Radiation Oncology, MGH and Harvard Medical School, Boston, MA 02114 USA.
Phys Med Biol. 2008 Aug 7;53(15):4137-51. doi: 10.1088/0031-9155/53/15/009. Epub 2008 Jul 17.
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 degrees 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.
最近的一项临床试点研究证明了离线正电子发射断层扫描/计算机断层扫描（PET/CT）范围验证用于质子治疗的可行性。体内PET测量受到血液灌注、组织成分变化、患者运动以及图像配准不确定性的挑战。除了这些生物学和治疗特定因素外，该方法的准确性还受到潜在物理过程的限制。本体模研究将物理因素与其他因素区分开来，评估PET/CT范围验证方法的可重复性、一致性和灵敏度。将扩展布拉格峰（SOBP）质子束输送到由聚甲基丙烯酸甲酯（PMMA）、肺等效材料板和骨等效材料板组成的体模中。在距离质子治疗单元步行10分钟路程内的商用PET/CT扫描仪上以列表模式采集PET数据。将测量的PET活度分布与基于Geant4和FLUKA蒙特卡罗（MC）代码的PET信号模拟结果进行比较。为了测试测量的PET信号的可重复性，比较了在体模中相同几何位置的两次独立测量的数据。此外，还比较了相同材料排列但在照射野内不同位置的激活深度剖面，以测试测量的PET信号的一致性。最后，研究了平行于束方向以及与束方向成6度角穿过空气/肺、空气/骨和肺/骨界面的激活深度剖面，以研究PET/CT范围验证方法的灵敏度。发现测量的PET信号的可重复性和一致性处于同一数量级。它们确定PET测量的物理精度约为1毫米。然而，在PET扫描仪的束边缘和视野（FOV）边缘，两次测量之间的范围差异高达2.6毫米，一次测量内的范围变化高达2.6毫米。研究发现PET/CT范围验证能够在存在复杂组织不均匀性的情况下检测到小的范围变化。这项研究表明了PET/CT验证方法在检测患者体内所输送剂量的全范围特征方面的物理潜力。
