Imaging in lung cancer: positron emission tomography scan

In the past 5 yrs, positron emission tomography (PET), usually used with 18F-fluoro-2-deoxy-glucose (FDG), has become an important imaging modality in lung cancer patients. Currently, the use of FDG-PET in respiratory oncology is mainly for diagnosis and staging. Standard indications are the evaluation of an indeterminate solitary pulmonary nodule or mass, where FDG-PET has proven to be significantly more accurate than computed tomography (CT) in the distinction between benign and malignant lesions. Several studies have also convincingly demonstrated that locoregional lymph node staging by FDG-PET (in correlation with CT images) is significantly superior to CT, with a negative predictive value equal or even superior to mediastinoscopy. FDG-PET also improves extrathoracic staging, through the detection of lesions missed at conventional imaging or characterization of lesions that remain equivocal on conventional imaging. Many European countries now have or plan reimbursement in these indications. Large-scale randomized studies should now focus on the impact this accurate tumour imaging technique has on treatment outcome and cost-efficacy. Ongoing studies in specialized centres focus on the use of FDG-PET in more advanced clinical applications, such as planning radiotherapy, response evaluation after radiotherapy or (induction) chemotherapy, follow-up and early detection of recurrence, and prognostic information in this in vivo measurement of tumour glucose metabolism. After a short note on the technique used and a summary of the current common indications of diagnosis and staging, this paper will deal mainly with two of the more advanced clinical applications of FDG-PET in locally advanced nonsmall cell lung cancer: radiation treatment planning and assessment of induction chemotherapy. Finally, it should be mentioned that a whole new field of applications of positron emission tomography in molecular biology, using new radiopharmaceutical probes, is under extensive investigation. These techniques are promising for future use in very early response monitoring during chemo- or radiotherapy, in evaluation of novel molecular-targeted lung cancer therapies, or even gene therapy.