Marks L B, Spencer D P, Sherouse G W, Bentel G, Clough R, Vann K, Jaszczak R, Coleman R E, Prosnitz L R
Department of Radiation Oncology, Duke University Medical Center, Durham NC 27710, USA.
Int J Radiat Oncol Biol Phys. 1995 Aug 30;33(1):65-75. doi: 10.1016/0360-3016(95)00091-C.
During thoracic irradiation (XRT), treatment fields are usually designed to minimize the volume of nontumor-containing lung included. Generally, functional heterogeneities within the lung are not considered. The three dimensional (3D) functional information provided by single photon emission computed tomography (SPECT) lung perfusion scans might be useful in designing beams that minimize incidental irradiation of functioning lung tissue. We herein review the pretreatment SPECT scans in 86 patients (56 with lung cancer) to determine which are likely to benefit from this technology.
Prior to thoracic XRT, SPECT lung perfusion scans were obtained following the intravenous injection of approximately 4 mCi of 99mcTc-labeled macro-aggregated albumin. The presence of areas of decreased perfusion, their location relative to the tumor, and the potential clinical usefulness of their recognition, were scored. Patients were grouped and compared (two-tailed chi-square) based on clinical factors. Conventional dose-volume histograms (DVHs) (DVFHs) are calculated based on the dose distribution throughout the computed tomography (CT)-defined lung and SPECT-defined perfused lung, respectively.
Among 56 lung cancer patients, decreases in perfusion were observed at the tumor, adjacent to the tumor, and separate from the tumor in 94%, 74%, and 42% of patients, respectively. Perfusion defects adjacent to the tumor were often large with centrally placed tumors. Hypoperfusion in regions separate from the tumor were statistically most common in patients with relatively poor pulmonary function and chronic obstructive pulmonary disease (COPD). Considering all SPECT defects adjacent to and separate from the tumor, corresponding CT abnormalities were seen in only approximately 50% and 20% of patients, respectively, and were generally not as impressive. Following XRT, hypoperfusion at and separate from the tumor persisted, while defects adjacent to the tumor improved in several patients. In four patients who achieved a complete response scored by CT with chemotherapy prior to XRT, persistent hypoperfusion was present at and adjacent to the tumor site in three. Among 30 patients with cancers not arising in the lung (14 breast, 12 lymphoma, 4 others), perfusion defects were seen in only 4 (2 adjacent and 2 apart). Recognition of decreases in perfusion mainly impacted on treatment planning for a few patients with poor pulmonary function and limited target volumes. DVFHs have been useful in beam selection for patients with marked perfusion heterogeneities.
Lung perfusion scans provide functional information not provided by CT scans that can be useful in designing radiation treatment beams that minimize incidental irradiation of the function regions of the lung. This approach appears to be most helpful in patients with gross intrathoracic lung cancer, especially those with small targets and relatively poor pulmonary function. One limitation of this approach is that some of the defects adjacent to the tumor site reperfuse following treatment, indicating that these scans identify perfusion rather than potential perfusion. Three dimensional functional data can be used to generate DVFHs that may be more predictive of the physiological consequences of the radiation than conventional DVHs. Additional work is currently underway to test this hypothesis.
在胸部放疗（XRT）期间，治疗野通常设计为尽量减少包含非肿瘤肺组织的体积。一般来说，肺内的功能异质性未被考虑在内。单光子发射计算机断层扫描（SPECT）肺灌注扫描所提供的三维（3D）功能信息可能有助于设计能尽量减少对功能性肺组织进行附带照射的射束。我们在此回顾了86例患者（56例肺癌患者）的治疗前SPECT扫描，以确定哪些患者可能从这项技术中获益。
在胸部XRT之前，静脉注射约4mCi的99mTc标记的大聚合白蛋白后进行SPECT肺灌注扫描。对灌注降低区域的存在情况、其相对于肿瘤的位置以及识别这些区域的潜在临床实用性进行评分。根据临床因素对患者进行分组并比较（双侧卡方检验）。分别基于在计算机断层扫描（CT）定义的肺和SPECT定义的灌注肺中的剂量分布计算常规剂量体积直方图（DVHs）（DVFHs）。
在56例肺癌患者中，分别有94%、74%和42%的患者在肿瘤处、肿瘤邻近处以及与肿瘤不相邻处观察到灌注降低。肿瘤邻近处的灌注缺损通常较大，尤其是肿瘤位于中央时。在肺功能相对较差和患有慢性阻塞性肺疾病（COPD）的患者中，与肿瘤不相邻区域的灌注不足在统计学上最为常见。考虑到与肿瘤相邻和不相邻的所有SPECT缺损，分别仅在约50%和20%的患者中观察到相应的CT异常，且通常不那么明显。XRT后，肿瘤处和与肿瘤不相邻处的灌注不足持续存在，而肿瘤邻近处的缺损在部分患者中有所改善。在XRT前通过化疗达到CT完全缓解的4例患者中，3例在肿瘤部位及其邻近处存在持续的灌注不足。在30例非肺癌患者（14例乳腺癌、12例淋巴瘤、4例其他肿瘤）中，仅4例（2例相邻和2例不相邻）出现灌注缺损。灌注降低的识别主要影响了少数肺功能差且靶体积有限的患者的治疗计划。DVFHs在为灌注异质性明显的患者选择射束方面很有用。
肺灌注扫描提供了CT扫描未提供的功能信息，这在设计能尽量减少对肺功能区域进行附带照射的放射治疗射束时可能有用。这种方法似乎对患有严重胸内肺癌的患者最有帮助，尤其是那些靶体积小且肺功能相对较差的患者。这种方法的一个局限性是，肿瘤部位邻近处的一些缺损在治疗后会重新灌注，这表明这些扫描识别的是灌注情况而非潜在灌注情况。三维功能数据可用于生成DVFHs，其可能比传统DVHs更能预测放疗的生理后果。目前正在进行更多工作来验证这一假设。
