Cattaneo G M, Rizzo G, Lombardi P, Ceresoli G, Savi A, Gilardi M C, Villa E, Calandrino R
Servizio di Fisica Sanitaria, Università degli Studi, Milano.
Radiol Med. 1999 Apr;97(4):272-8.
Single photon emission computed tomography (SPECT) of lung perfusion permits to map functioning lung parenchyma with higher sensitivity than CT. Delivering higher radiation doses is used to increase local control in lung carcinoma; this strategy is based on radiobiological and clinical studies. Lung parenchyma is a dose-limiting tissue in patients irradiated for lung cancer. Functional mapping based on SPECT and CT findings permits to design radiation beams such as to minimize irradiation of functioning lung.
CT and SPECT were used to examine a patient with non small cell lung carcinoma (stage IIIB, T4N0, left lung) candidate to conformal irradiation. Images were spatially correlated based on lung contours and using CT findings as reference. SPECT images were normalized to mean right lung value and expressed as perfusion (functional) contours. CT images and perfusion contours were transferred to the treatment planning system (Cadplan V 2.79, Varian-Dosetek Oy): in this way both functional (SPECT) and anatomical (CT) data were available for planning. A comparison was made between two irradiation techniques defined at TPS with (technique B) or without (technique A) SPECT contour information. The prescribed dose was 70.2 Gy. Rival plans were compared using dose volume histograms of target and risk organs. Both functional and anatomical regions were considered in the lung, together with single lung(s) and lung parenchyma. A second perfusion SPECT was obtained 5 months after irradiation and correlated with pretreatment CT images.
SPECT lung scans showed marked heterogeneity in the left lung, which was found neither at CT nor at classic lung function tests. The lung volume with perfusion exceeding 80% of average corresponds to about 70% of the anatomical volume. Mean doses to anatomical and to functional lung parenchyma were 24 Gy and 19 Gy, respectively, with technique A and 23 Gy and 18 Gy, respectively, with technique B. Thirty-five percent and 20%, respectively of anatomical and functional lung parenchyma received > or = 25 Gy (V25) with technique B. The figure for functional lung parenchyma was reduced by 5% with technique B. Optimal design of irradiation field geometry decreased the area of functional parenchyma given high doses, which sparing was greater with smaller irradiation volumes.
We have integrated the functional data provided by SPECT lung perfusion into a commercial irradiation planning system. Lung function mapping permits to design irradiation portals sparing larger areas of functional lung parenchyma.
肺灌注单光子发射计算机断层扫描（SPECT）能够绘制出功能正常的肺实质图，其敏感性高于CT。给予更高的辐射剂量用于提高肺癌的局部控制率；这一策略基于放射生物学和临床研究。肺实质是肺癌放疗患者的剂量限制组织。基于SPECT和CT结果进行功能映射，有助于设计放射线束，从而尽量减少对功能正常肺组织的照射。
使用CT和SPECT对一名非小细胞肺癌（ⅢB期，T4N0，左肺）拟进行适形放疗的患者进行检查。基于肺轮廓并以CT结果为参考，对图像进行空间配准。SPECT图像以右肺平均数值进行归一化处理，并表示为灌注（功能）轮廓。将CT图像和灌注轮廓传输至治疗计划系统（Cadplan V 2.79，Varian-Dosetek Oy）：通过这种方式，功能（SPECT）和解剖（CT）数据均可用于治疗计划制定。在治疗计划系统中定义了两种放疗技术并进行比较，技术B使用SPECT轮廓信息，技术A不使用。处方剂量为70.2 Gy。使用靶区和危及器官的剂量体积直方图对竞争计划进行比较。在肺内，同时考虑功能和解剖区域，以及单肺和肺实质。放疗后5个月进行第二次灌注SPECT检查，并与放疗前CT图像进行配准。
SPECT肺扫描显示左肺存在明显的异质性，这在CT检查和经典肺功能测试中均未发现。灌注超过平均水平80%的肺体积约占解剖体积的70%。技术A时，解剖学肺实质和功能性肺实质的平均剂量分别为24 Gy和19 Gy；技术B时，分别为23 Gy和18 Gy。技术B时，解剖学肺实质和功能性肺实质分别有35%和20%接受≥25 Gy（V25）的剂量。技术B时，功能性肺实质的这一比例降低了5%。优化照射野几何形状可减少高剂量照射的功能性实质面积，照射体积越小，这种 sparing效果越明显。
我们已将SPECT肺灌注提供的功能数据整合到商业放疗计划系统中。肺功能映射有助于设计放疗射野，从而使更大面积的功能正常肺实质免受照射。
