Department of Medical Radiation Physics, Karolinska Institutet and Stockholm University, Stockholm, PO Box 260, SE-171 76, Sweden.
EJNMMI Res. 2013 Jan 23;3(1):6. doi: 10.1186/2191-219X-3-6.
The purpose of this work was to reveal the research interest value of positron emission tomography (PET) imaging in visualizing the induced tissue activity post high-energy photon radiation treatment. More specifically, the focus was on the possibility of retrieving data such as tissue composition and physical half-lives from dynamic PET acquisitions, as positron-emitting radionuclides such as 15O, 11C, and 13N are produced in vivo during radiation treatment with high-energy photons (>15 MeV). The type, amount, and distribution of induced positron-emitting radionuclides depend on the irradiated tissue cross section, the photon spectrum, and the possible perfusion-driven washout.
A 62-year-old man diagnosed with prostate cancer was referred for palliative radiation treatment of the pelvis minor. A total dose of 8 Gy was given using high-energy photon beams (50 MV) with a racetrack microtron, and 7 min after the end of irradiation, the patient was positioned in a PET/computed tomography (CT) camera, and a list-mode acquisition was performed for 30 min. Two volumes of interests (VOIs) were positioned on the dynamic PET/CT images, one in the urinary bladder and the other in the subcutaneous fat. Analysis of the measured relative count rate was performed in order to compute the tissue compositions and physical half-lives in the two regions.
Dynamic analysis from the two VOIs showed that the decay constants of activated oxygen and carbon could be deduced. Calculation of tissue composition from analyzing the VOI containing subcutaneous fat only moderately agreed with that of the tabulated International Commission on Radiation Units & Measurements (ICRU) data of the adipose tissue. However, the same analysis for the bladder showed a good agreement with that of the tabulated ICRU data.
PET can be used in visualizing the induced activity post high-energy photon radiation treatment. Despite the very low count rate in this specific application, wherein 7 min after treatment was about 5% of that of a standard 18F-FDG PET scan, the distribution of activated tissue elements (15O and 11C) could be calculated from the dynamic PET data. One possible future application of this method could possibly be to measure and determine the tumor tissue composition in order to identify any hypoxic or necrotic region, which is information that can be used in the ongoing therapy planning process.
The official name of the trial committee of this study is 'Regionala etikprövningsnämnden i Stockholm' (FE 289, Stockholm, SE-17177, Sweden). The unique identifying number is 2011/1789-31/2.
本研究旨在揭示正电子发射断层扫描（PET）成像在可视化高能光子辐射治疗后诱导组织活性方面的研究兴趣价值。更具体地说，研究重点是从动态 PET 采集数据中获取组织成分和物理半衰期等信息的可能性，因为在高能光子（>15 MeV）辐射治疗过程中，体内会产生正电子发射放射性核素，如 15O、11C 和 13N。诱导产生的正电子发射放射性核素的类型、数量和分布取决于受照射组织的横截面积、光子谱以及可能的灌注驱动清除。
一名 62 岁男性被诊断患有前列腺癌，拟行骨盆小剂量姑息性放疗。采用轨道微管的高能光子束（50 MV）给予 8 Gy 总剂量，照射结束后 7 分钟，患者被置于 PET/计算机断层扫描（CT）相机中，进行 30 分钟的列表模式采集。在动态 PET/CT 图像上定位了两个感兴趣容积（VOI），一个位于膀胱，另一个位于皮下脂肪。对测量的相对计数率进行分析，以计算两个区域的组织成分和物理半衰期。
来自两个 VOI 的动态分析表明，可以推断出活性氧和碳的衰减常数。仅分析包含皮下脂肪的 VOI 来计算组织成分，与列于国际辐射单位和测量委员会（ICRU）脂肪组织数据的结果仅中度一致。然而，对膀胱的相同分析结果与列于 ICRU 数据的结果非常一致。
PET 可用于可视化高能光子辐射治疗后的诱导活性。尽管在这种特定应用中，治疗后 7 分钟的计数率非常低，约为标准 18F-FDG PET 扫描的 5%，但仍可以从动态 PET 数据中计算出激活组织元素（15O 和 11C）的分布。该方法的一个可能的未来应用可能是测量和确定肿瘤组织成分，以识别任何缺氧或坏死区域，这些信息可用于正在进行的治疗计划过程。
本研究的试验委员会的官方名称为 'Regionala etikprövningsnämnden i Stockholm'（FE 289，Stockholm，SE-17177，Sweden）。独特的识别号为 2011/1789-31/2。
