Multiple studies have shown that FDG-PET is more sensitive and specific than CT in detecting stages N2 and N3 disease, with some false-positive results due to inflammatory adenopathy, usually related to granulomatous disease. A recent study reported a sensitivity and specificity of 89% and 99%, respectively, for PET imaging of stages N2 and N3 adenopathy, compared with 57% and 94%, respectively, for CT. Clearly, adopting PET to assess mediastinal disease in the staging of lung cancer reduces costs and morbidity by sparing patients from unnecessary surgery. A recent report showed that PET imaging uncovered 29% additional lesions, which led to alterations in management in 41% of patients, thereby eliminating surgery in 18% of the population.
FDG-PET is also useful for differentiating recurrent lung cancer from postoperative or postradiation changes, including radiation pneumonitis (Fig 10). In this setting, both visual inspection and SUV analysis appear to provide useful results. Some investigators have found that an SUV of > 2.5 is sufficiently sensitive and specific for tumor, while others recommend higher values, such as 5.0, in order to improve the specificity while maintaining sensitivity of > 90%. Clearly, PET will serve an increasingly important role in patients whose CT or MR scans prove indeterminate for recurrent or residual tumor following radiation, surgery, or both. itat on
Recently, we reported preliminary data on the role of FDG-PET imaging in the management of malignant mesothelioma. The uptake of FDG was significantly higher in malignant pleural lesions than in benign abnormalities. The overall sensitivity and specificity of PET were 91% and 100%, respectively. Recent studies also have shown that PET reveals additional sites of disease involvement, not demonstrated by CT, in both non-Hodgkin’s lymphoma and Hodgkin’s disease. A preliminary cost-effectiveness analysis which substituted whole body PET for routine CT and MR scans revealed a substantial savings during initial staging and restaging of Hodgkin’s disease and non-Hodgkin’s lymphoma.
Clearly, FDG-PET provides valuable information for the management of patients with lung cancer, lung nodules, and mesotheliomas. In this era of cost containment and “evidence-based” medicine, the data support the use of PET in these settings. The breadth of applications for FDG-PET is staggering, and its role in a variety of oncologic settings, including lymphoma and esophageal cancer, is becoming evident. The potential of its application to sarcoid and other inflammatory diseases is also rapidly becoming evident. The role of PET in gene therapy as a molecular imaging technique is in its infancy, but appears promising.
Unfortunately, very few medical centers in the world have access to this technology despite its proven efficacy. Since January 1998, Medicare has approved reimbursement for staging of lung cancer and characterizing lung nodules by PET. Recognition by Medicare as a cost-effective technique further consolidates the position of PET as a powerful tool in thoracic imaging.
Figure 10. PET scan in patient with lung cancer. Top, left: CT image revealing a right lung Pancoast tumor in a 62-year-old man who underwent radiation and chemotherapy in preparation for a curative surgery. Top, right: a repeat CT scan (the image on the right) prior to surgery demonstrated two new nodules in the right lung field. The degree of the disease activity of the original tumor and the nature of the new lesions were uncertain at this time. Bottom: a PET-FDG scan of the chest and abdomen (selected coronal planes are shown above) revealed moderate metabolic activity in the lateral (arrowhead) and medial (solid arrow) aspects of the primary tumor, respectively. These findings suggested that the primary tumor was still active in spite of chemotherapy and radiation therapy (XRT). The two lesions in the lower right lung were also active (broken arrows) and were indicative of a malignant process. Bottom, left: in addition, at least two lumbar vertebral bodies appeared to have metastatic lesions. Again, by performing PET-FDG imaging, the extent of the disease activity was more accurately determined than that estimated by state-of-the-art anatomic imaging techniques.