FDG-PET is particularly accurate in detecting malignant pulmonary lesions. Lung cancer shows a high uptake of FDG, whereas background activity in the normal lung and mediastinum is generally low. Numerous studies have demonstrated that FDG-PET is the most accurate noninvasive method of detecting and staging lung cancer. The evaluation of solitary pulmonary nodules was one of the earliest applications of FDG-PET for extracranial tumors. Prospective studies have shown that FDG-PET has both sensitivity and specificity of approximately 90% in the evaluation of solitary pulmonary nodules (Coleman 1999; Marom et al. 2000).
False-positive findings are caused by inflammatory processes, such as tuberculomas, aspergillosis, and coccidioidomycosis. Accordingly, the specificity of FDG-PET tends to be lower in countries where these diseases are endemic.
False-negative findings can be due to several factors: for example the sensitivity of current PET scanners for lesions with a diameter of less than 1 cm is lower than for larger lesions owing to partial volume effects. More importantly, some subtypes of malignant tumors, e.g. carcinoids and bronchioloalveolar carcinomas, show only a small amount of FDG accumulation and may give false-negative results despite being greater than 1 cm in diameter (Erasmus et al. 1998; Higashi et al. 1998). Kalff et al. prospectively studied the impact of FDG-PET on the clinical management of 105 patients with NSCLC (Kalff et al. 2001). Indications for PET were primary staging (n = 59), restaging (n = 34), and suspected malignancy, subsequently confirmed as NSCLC (n =12). In 27 (26%) of the 105 cases, PET results led to a change from curative to palliative therapy after up-staging of disease extent. PET appropriately down-staged 10 of 16 patients initially scheduled for palliative therapy, allowing potentially curative treatment in 4 patients and no treatment in 6 patients. PET influenced the radiation delivered in 22 (65%) of 34 patients who subsequently received radical radiotherapy. Twelve patients considered "probably inoperable" on conventional imaging studies were down-staged by PET and underwent potentially curative surgery. PET missed only 1 primary tumor, which was a 5mm scar carcinoma.
CT and PET understaged 3 of 20 surgical patients, 2 with N1 lesions (<5 mm) and 1 with un recognized atrial involvement, and PET failed to detect 1 small intrapulmonary metastasis that was apparent on CT. No pathological N2 disease was missed by PET. FDG-PET changed or influenced management decisions in 70 patients (67%) with NSCLC: patients were frequently spared unnecessary treatment, and management was more appropriately targeted. However, FDG-PET cannot be seen as a replacement for invasive diagnostic procedures.
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