PET Scans and Technology Assessment

Abstract

FEW DIAGNOSTIC TECHNOLOGIES DEPLOYED DURING THE past 3 decades have had as profound an impact on clinical medicine as computed tomography (CT) and magnetic resonance imaging (MRI). While these technologies have improved case management, they have also become a billion-dollar industry that has had a major impact on rising health care costs. It is concerning, therefore, that these expensive technologies have been widely adopted before being adequately evaluated. With the emergence of positron emission tomography (PET) from research laboratories into routine clinical use, physicians are faced once again with a new technology that promises to deliver more but that also costs more. At the current Medicare reimbursement rate of approximately $2000 per PET scan, unfettered use of this technology would easily add billions of dollars in spending to an already stressed health care financing system. Positron emission tomography is a nuclear medicine imaging technique that uses radiopharmaceuticals— typically, a radionuclide-labeled analog of glucose, fluorodeoxyglucose (FDG)—to detect abnormal metabolic activity. Since malignant tumors usually have increased cellular metabolism and, thus, increased glucose metabolism, PET is able to localize malignant tissue. By providing information on function and metabolism, PET may complement traditional imaging modes such as CT and MRI, which provide information on anatomical structures. In addition to its ability to distinguish benign and malignant processes based on differences in biological activity, PET has the ability to examine the whole body for both primary malignancies and metastatic disease in a single procedure. Positron emission tomography was developed in the 1970s and whole-body imaging became possible in the mid1980s. In 1995, Medicare reimbursement for specific diagnostic uses of PET began. Use of FDG-PET for characterization of suspected solitary pulmonary nodules (SPNs) to plan treatment was begun in 1998. Medicare coverage for FDG-PET was recently broadened after a request was made to the Health Care Financing Administration (HCFA). Several additional indications were added from a submitted list of 22 diseases and disorders. It is important to consider how to evaluate promising emerging technologies in light of existing technologies. After safety considerations, the basic issue in the evaluation of any new diagnostic technology focuses on the test performance, typically measured as sensitivity and specificity. Although numerous studies have been published on diagnostic technologies, many do not truly evaluate diagnostic performance, provide no useful information, or are of poor methodological quality. To help understand the literature, systematic review has become the standard approach to evaluate and summarize clinical evidence. As part of the critical evaluation of the evidence, a comprehensive search for and critical appraisal of the studies are performed. Meta-analyses are then performed to provide quantitative results and allow meaningful comparisons of competing technologies. In this issue of THE JOURNAL, Gould and colleagues report their meta-analysis of the diagnostic accuracy of FDG-PET for evaluation of pulmonary lesions. The authors identified 34 studies in their systematic review of the literature that were suitable for inclusion in the meta-analysis. None of the evaluated studies met all of the established quality criteria, and only 14 studies satisfied 70% to 80% of the criteria. The evaluated studies reported a range of sensitivity between 83% and 100% but had specificities ranging from 0% to 100%, which raises doubts about the reliability of this test. The summary estimates of test sensitivity and specificity to detect malignancy in all focal pulmonary lesions were 96.0% and 73.5%, respectively. Gould and colleagues allude to the important issue of testing thresholds, ie, pretest probability of disease at which the results of the diagnostic test may affect treatment. In patients with sufficiently low probability of disease, a positive test result may not sufficiently increase the likelihood of disease to warrant treatment or further evaluation (eg, if a positive test result increases the likelihood of cancer from 1% to 2%). But patients with sufficiently high probability of disease should receive treatment regardless of test findings. In patients with a high pretest probability of malignant disease (eg, 80%), the posttest probability of malignancy with a negative PET result is about 14%. In these patients, regardless of PET results, further evaluation would likely be needed. Use of PET should be limited to patients for whom the test will likely