Coleman R E
Duke University Medical Center, Durham, NC 27710.
Cancer. 1991 Feb 15;67(4 Suppl):1261-70. doi: 10.1002/1097-0142(19910215)67:4+<1261::aid-cncr2820671524>3.0.co;2-l.
Single photon emission computed tomography (SPECT) and positron emission tomography (PET) are now being used to improve the information available from radioisotopic imaging of patients with cancer. These nuclear medicine techniques offer the potential for studying regional function and biochemistry by using radiolabeled substrates. The chemical changes of malignancy precede anatomic changes, and PET and/or SPECT may detect these changes before anatomic changes have occurred. The superiority of SPECT compared with planar imaging has been demonstrated for cardiac and brain imaging. Radiopharmaceuticals containing technetium 99 m (99mTc) are best suited for SPECT imaging because large amounts of radioactivity are administered and the collimator-camera systems are optimized for the 140 keV photons of 99mTc. The current interest in imaging cancer with SPECT relates to the use of gallium 67 citrate and monoclonal antibodies labeled with iodine 123 or indium 111. SPECT can image these radioisotopes, but the advantages compared with planar imaging have not been clearly defined. Furthermore, the ability to quantitate the distribution of single photon emitters other than 99mTc has not been demonstrated. New SPECT systems with three heads or rings of detectors offer promise for improved, quantitative imaging. PET has the capability of imaging tracers with the biologically important elements C-11, N-13, O-15, and F-18 used for positron labeling. These radioisotopes have short half-lives and require a cyclotron close to the PET facility. The most prominently used radiopharmaceutical for PET is F-18 fluorodeoxyglucose (FDG). PET studies with FDG in patients with primary brain tumors have demonstrated the ability to determine the degree of malignancy, to differentiate necrosis from recurrent tumor after radiation therapy or chemotherapy, and to predict prognosis. Other metabolic functions of cancer have been studied, including amino acid accumulation, thymidine uptake, oxygen utilization, intermediary metabolism, and receptor status. PET has the potential to make a major impact on the characterization of a malignancy and the effect of therapy.
单光子发射计算机断层扫描（SPECT）和正电子发射断层扫描（PET）目前正被用于改善癌症患者放射性核素成像所提供的信息。这些核医学技术通过使用放射性标记底物，为研究局部功能和生物化学提供了可能。恶性肿瘤的化学变化先于解剖学变化，PET和/或SPECT可能在解剖学变化发生之前检测到这些变化。SPECT与平面成像相比在心脏和脑成像方面的优越性已得到证实。含锝99m（99mTc）的放射性药物最适合SPECT成像，因为给予了大量放射性，且准直器 - 相机系统针对99mTc的140keV光子进行了优化。目前利用SPECT对癌症进行成像的研究兴趣在于使用枸橼酸镓67以及用碘123或铟111标记的单克隆抗体。SPECT能够对这些放射性核素进行成像，但与平面成像相比的优势尚未明确界定。此外，对99mTc以外的单光子发射体分布进行定量的能力尚未得到证实。具有三个探测器头或探测器环的新型SPECT系统有望实现改进的定量成像。PET能够对使用用于正电子标记的具有生物学重要意义的元素C - 11、N - 13、O - 15和F - 18的示踪剂进行成像。这些放射性核素半衰期短，需要在PET设备附近配备回旋加速器。PET最常用的放射性药物是F - 18氟脱氧葡萄糖（FDG）。对原发性脑肿瘤患者进行的FDG PET研究已证明其能够确定恶性程度，区分放疗或化疗后坏死与复发肿瘤，并预测预后。癌症的其他代谢功能也已得到研究，包括氨基酸积累、胸腺嘧啶摄取、氧利用、中间代谢和受体状态。PET有可能对恶性肿瘤的特征描述和治疗效果产生重大影响。
