The Role of 18F-FDG-PET/CT Scan in Lung Cancer Patients

Overview

Describe strengths and limitations of FDG PET/CT for staging. Evaluate the utility of PET/CT in assessment of therapy response and restaging

Lung cancer is one of the most common cancers and it represents the main cause of cancer mortality worldwide. It is histopathological classified into main groups: Small cell lung cancer (15%) and Non-small cell lung cancer (85%). NSCLCs are generally subcategorized into adenocarcinoma, squamous cell carcinoma (SqCC), and large cell carcinoma. Positron emission tomography (PET) is now an important cancer imaging tool, both for diagnosis and staging, as well as offering prognostic information based on response. PET sets the gold standard in the evaluation of an indeterminate solitary pulmonary nodule or mass, where PET has proven to be significantly more accurate than computed tomography (CT). For NSCLC chest CT is the standard imaging modality for assessing primary tumor size and identifying its margins. PET-CT may be helpful in assessing a nodule located in same lobe. It can also provide information on parietal or mediastinal involvement. PET is useful for differentiating tumor tissue from atelectasis, which may be helpful if radiotherapy is planned to determine the target volume . In the evaluation of metastatic spread to loco-regional lymph nodes, PET is significantly more accurate than CT, so that invasive surgical staging may be omitted in many patients with negative mediastinal PET images. In patients with positive mediastinal PET images, invasive surgical staging remains mandatory because of the possibility of false-positive findings due to inflammatory nodes or granulomatous disorders. Forty percent of patients with NSCLC have distant metastases at presentation, most commonly in the adrenal glands, bones, liver, or brain . In the search for metastatic spread, PET is a useful adjunct to conventional imaging. This may be due to the finding of unexpected metastatic lesions or due to exclusion of malignancy in lesions that are equivocal on standard imaging. However, at this time, PET does not replace conventional imaging. The diagnostic accuracy of initial pre-therapy PET-CT results in improved staging, and thus is of high prognostic value. Many studies conducted the value of using semi-quantitative measures as metabolic tumor volume (MTV) and Total lesion glycolysis (TLG) in predicting prognosis and survival rather than the traditional method of measuring Standard uptake value (SUV). Several studies have demonstrated that PET imaging proves useful for assessing the response to chemo therapy or targeted therapy in patients with metastatic NSCLC.

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