Brazilian experience in characterization of solitary pulmonary nodules using 18-fluorodeoxyglucose on camera-based PET

Introduction: Positron emission tomography (PET) using 18-fluorodeoxyglucose (18F-FDG), showing increased 18F-FDG uptake and retention in malignant cells, has proved useful to differentiate malignant from benign pulmonary nodules. An accurate diagnosis of pulmonary cancer represents a clinical challenge. This could be even more significant in Latin America, where the incidence of infectious granulomas is high. However, the high cost of dedicated- PET studies has prevented widespread application of this technique. Hybrid PET is a new approach to tumor imaging using 18F-FDG. In our country, such a system was introduced in 1998. These systems offer the possibility to produce diagnostic quality images of 18F-FDG body distribution, making metabolic scans potentially available. Objective : The aim of this study was to determine the diagnostic value of F-18-FDG scan using a hybrid PET in characterizing pulmonary nodules as benign or malignant. Methods: We evaluated 62 patients (50 male, 38-79y) with indeterminate solitary pulmonary nodules after computed tomography (CT) screening. 18F-FDG scans were performed on a camera-based PET (MCD Vertex-plus Adac) after injection of 18-F-fluorodeoxyglucose intravenously. Image acquisition began after 1 hour. Qualitative analysis of the images was performed by visual identification of areas of increase (positive) or absence (negative)of FDG uptake. All results were assessed on basis of histology or clinical/radiological follow-up. Results : Twenty-one patients (33.9%) showed a marked increase in FDG uptake and underwent invasive intervention (biopsy or thoracotomy). Histopathological evaluation revealed malignant disease in eighteen of these patients and benign disease in three of them (positive predictive value = 85.7%). Forty-one patients (66.1%) showed absence of FDG uptake. Fourteen of them underwent surgical procedure. Malignancy was found in only one. Twenty-seven patients with negative FDG studies are being followed up with a CT scan every 4 or 6 months. None of them has shown any changes in morphological characteristics of the nodule so far. The negative predictive value of F-18-FDG imaging was 97.5% and accuracy was 93.5%. Conclusion: This study suggests that F-18-FDG on camera-based PET may help to differentiate malignant from benign solitary pulmonary nodules. Therefore, it can avoid unnecessary procedures, reducing morbidity/ mortality and costs