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Positron Emission Tomography Imaging of Lung Cancer


Summary of Key Points

  • 18 F-2-deoxy- d -glucose (FDG)-positron emission tomography–computed tomography (PET–CT) is routinely used clinically for diagnosis, staging, and radiation treatment planning and may have a role in prognosis and monitoring of treatment response.

  • FDG-PET–CT is not optimal in determination of T descriptors (additional small lung nodules, locoregional invasion, etc.) as respiratory motion and or low-radiation-dose imaging degrade image quality.

  • FDG-PET–CT has superior accuracy compared with CT in detecting hilar (N1), mediastinal (N2, N3), and extrathoracic (N3) nodal metastasis.

  • FDG-PET–CT has superior accuracy compared with CT in detecting M1b and M1c (extrathoracic) metastasis.

  • FDG-PET–CT detection of occult metastasis (M1b/M1c) increases as T and N descriptors increase and impact on management is greater in patients with more advanced disease.

  • FDG uptake threshold such as standardized uptake value (SUV) is unreliable in differentiating inflammatory from metastatic disease.

  • FDG-PET prognostic information is not dependable and may be confounded by limitations of SUV reproducibility.

  • FDG-PET–CT metabolic tumor volume and total lesion glycolysis (which take into account tumor size and uptake of FDG) may be important prognostic factors.

  • FDG-PET–CT may allow an early and sensitive assessment of antitumor effect after therapy.

  • FDG-PET–CT improves accuracy of target delineation in radiation treatment planning.

  • A PET–CT-defined tumor target is usually smaller than that defined by CT, and incorporation of PET–CT into radiotherapy planning can allow radiation-dose escalation without increasing side effects.

  • FDG is the only Medicare-approved PET–CT tracer for evaluation of cancer.

  • Novel PET radiotracers that interrogate different metabolic pathways beyond glycolysis, receptors, and targets are being evaluated in staging, response evaluation, and targeted therapy assessment.

PET using the radiopharmaceutical FDG, a d -glucose analog labeled with fluorine-18, complements conventional radiographic imaging for the evaluation of patients with nonsmall cell lung cancer (NSCLC). FDG-PET has an important role in the staging of NSCLC according to the tumor, node, and metastasis (TNM) system and is routinely used to improve the detection of nodal and extrathoracic metastases. FDG-PET is also currently used to improve the planning of radiation therapy and is being evaluated for the assessment of prognosis and therapeutic response. By potentially allowing for an earlier and more sensitive assessment of the effect of antitumor therapy, FDG-PET may be predictive of the outcome of treatment and the survival of patients after treatment. This chapter will discuss the use of FDG-PET for the staging of disease, the planning of radiation therapy, and the assessment of outcome and prognosis, with an emphasis on the appropriate clinical use of FDG-PET for the treatment of patients who have NSCLC. In addition, the use of novel radiotracers that interrogate different metabolic pathways, receptors, and targets to overcome the potential limitations of FDG-PET in staging, as well as early response evaluation and monitoring of response to targeted therapies, will be reviewed.

Staging of Lung Cancer

Size, Location, and Locoregional Invasion (T Descriptor)

FDG-PET is used together with CT because the integration of metabolic activity with the high-spatial resolution of CT is important for the evaluation of tumors in terms of size, location, and the degree of locoregional invasion (T descriptor) as well as for the determination of the anatomic location of regions of focally increased FDG uptake. It is important to be aware that the relatively poor spatial resolution of PET limits its utility for the evaluation of the primary tumor. However, the CT component of integrated PET–CT also has shortcomings in terms of its ability to accurately demonstrate T descriptors such as the presence of additional small lung nodules and locoregional invasion as it is often performed during respiration and with a low-radiation-dose imaging protocol, both of which can compromise image quality. Nevertheless, FDG-PET improves the detection of nodal and distant metastases and frequently alters the treatment of patients. Accordingly, this review of TNM staging will focus on the important role of PET imaging for the detection of nodal and distant metastases at the time of initial staging according to the seventh edition of the American Joint Committee on Cancer TNM staging system and will reference the proposals for the forthcoming eighth edition when applicable.

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