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pet fact sheet 699 2 - University of Kansas Flipbook PDF
Knowledge of the stage of the disease is therefore critical before a patient is exposed to the potentially unnecessary r
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PET FACT SHEET
In the dramatically changing world of diagnostic imaging the current revolution taking place in Nuclear Medicine is among the most exciting. The development of whole-body Positron Emission Tomography (PET), together with the imaging agent 18F fluorodeoxyglucose (FDG) enables the accurate non-invasive detection and staging of cancer. Pioneered by scientists at UCLA and developed by CTI PET Systems, Inc., this technology has resulted in a convincing body of knowledge that can now be applied to benefit patients with cancer. With the increasing availability of commercially manufactured FDG, there is a growing body of evidence that whole-body PET imaging is advantageous for patient care quality and cost-effective patient management. PET offers a comprehensive assessment for both the initial staging of newly diagnosed cancers, ranging from lymphoma to lung tumors, as well as in treatment. The extent and stage of disease can be determined accurately to enable a rational decision for patient management. PET was developed in the late 1960’s, but recent developments have resulted in its recognition as an invaluable clinical test for tumor imaging. No other imaging modality has comparable potential because PET has the unique ability to image functional processes, such as tumor metabolic activity, in vivo. The basic principals of PET are based on the detection of photons emitted from the patient after the intravenous injection of a short-lived radiopharmaceutical (18F or FDG, a sugar analogue). These photons are detected by the PET scanner and allow the reconstruction of a three dimensional image of the glucose metabolism in the body. The ability to image glucose metabolism non-invasively is important, because most malignant tumors exhibit a high glucose metabolic activity (1,2). The most recent feature of PET is the capability to acquire tomographic whole-body images. Whole-body PET images can be displayed in transaxial, coronal, or sagittal image planes. The images from the first prototype, developed by Drs. Michael Phelps and Edward Hoffman at UCLA, took one and a half days to reconstruct. Today, the same reconstruction takes only a few minutes. The results are 3-dimensional images of the body which can be used to localize normal and abnormal processes, providing clinicians with information about the tissue biochemistry that is unobtainable by other imaging modalities. Anatomical imaging procedures such as CT or MRI frequently cannot distinguish between malignant disease and invasive tissue biopsies are frequently the only means to assess the nature of a tumor. The patient should fast after midnight on the day prior to the study. The patient receives an intravenous injection of the radiopharmaceutical FDG. The actual scan begins approximately 45 minutes to one hour later to allow sufficient time for the tracer to accumulate in abnormal tissue. While lying on a comfortable table, the patient is moved slowly through the scanner to obtain images of the entire body. There are no side effects to this procedure and the amount of radiation injected is well within the safe levels. The scans take about 60 to 90 minutes. The PET images are created with the help of three technologies: • the cyclotron, which produces safe radioisotopes. • the scanner, which records the location of the radio tracer as it accumulates in different tissues in the body and • a computer, which reconstructs the signals into 3-dimensional images of the body. A large body of literature indicated that FDG-PET scanning is useful to differentiate malignant from benign tumors, as well as to determine the extent and stage of cancer. This of paramount importance to guide physicians to the best therapeutic approach i.e., chemotherapy vs. radiation therapy vs. surgery. In up to 15% of patients, PET will detect otherwise unsuspected metastatic disease, which alters the treatment strategy. PET is also unique in its capability to differentiate between residual scar tissue, radiation necrosis and tumor recurrence and, in some cases may be useful in assessing the patients progress in a given therapeutic regimen. Research shows PET to be useful to detect or stage these types of cancer: Solitary Pulmonary Nodule The nature of a solitary pulmonary nodule can be determined with high accuracy using FDG-PET imaging. For nodules greater than 1 centimeter in diameter the overall sensitivity and specificity are 83 and 90%, respectively. In contrast, the nature of such solitary nodules cannot be determined with anatomical imaging modalities such as CT or MRI. Moreover, PET imaging is a non-invasive method and thus not associated with any morbidity as compared to lung biopsy. (3,4) Lung Cancer The overall sensitivity and specificity of FDG-PET for detecting lung cancer is on the order of 90%. In addition to the detection o f disease, the metastatic spread of the disease can be determined, which has important implications for patient management. This is particularly important in non-small cell lung cancer, where a cure can be achieved only by complete surgical resection of the tumor. Tumor involvement of the mediastinum at the time of initial diagnosis carries a poor prognosis (five-year survival rates of only 5-10%). In contrast, if the mediastinum is free of disease, the 5-year survival approached 40%.
Knowledge of the stage of the disease is therefore critical before a patient is exposed to the potentially unnecessary risk of thoracotomy. Recent prospective studies confirm that PET is significantly more accurate than CT for staging mediastinal involvement. The accuracy was reported to be 85% for PET but only 52% for CT. There are several reasons for the superiority of PET: •
High FDG uptake signifies malignancy event in normally sized lymph nodes (i.e.,