CHARACTERIZATION OF CHEST MASSES BY FDG POSITRON EMISSION TOMOGRAPHY

Radiographic imaging techniques have proved to be of limited value in characterizing chest masses, Likewise, scintigraphic techniques with t umor-seeking single photon emitting agents have shown marginal practic al benefit. In contrast, high resolution PET with [F-18]-2-fluoro-5-D- deoxyglucose (FDG) offers a unique opportunity to distinguish benign f rom malignant processes by determining metabolic characteristics. PET scan results, including graphical analysis of tumor transfer constants (Patlak plot) in 21 patients with primary lung cancer, were compared to clinical outcome (histologic proof or clinical follow-up of longer than 1 year) in 54 patients who had chest masses identified by CT and/ or plain film. The patients were categorized into three groups. The fi rst group (N = 23) had primary, unknown, lung masses. Differentiation of benign from malignant tumors by PET had a sensitivity of 100% and a specificity of 67%. The second group (N = 13) had proven lung carcino ma or lymphoma and post-therapy PET scanning for recurrent tumor. In t his setting, PET had a sensitivity of 83% and a specificity of 80%. Th e third group (N = 18) had extrathoracic malignancies and suspected pu lmonary metastases. Metastatic lesions were identified with a sensitiv ity of 87% and specificity of 83%. Glucose uptake by normal tissue is variable and inflammatory/infectious processes can have high FDG uptak e and overlap with the glucose uptake of malignant tissue. FDG PET is useful in characterizing chest tumors based on the level of their meta bolic activity. Malignant tissue has a high glucose uptake. Elevated F DG uptake by an active inflammatory process may produce overlapping re sults. Despite this shortcoming, PET can help to separate benign from mast malignant lung lesions, to confirm lung metastases, and to monito r the therapy of chest neoplasms.