PET Scanning in Staging and Evaluation of Response to Treatment in Lung Cancer

Abstract

Positron emission tomography (PET) represents the most signifi cant advance in lung cancer imaging since the introduction of computed tomography (CT) (Stroobants et al. 2003) and is having an increasing impact on the management of lung cancer patients who are candidates for radiotherapy (Hicks and MacManus 2003). Modern PET scanners can produce three-dimensional images of the distribution of the positron emitting isotopes in humans and animals with a resolution previously unseen in nuclear medicine. These images allow direct qualitative and quantitative analyses of a range of metabolic processes in tumours and normal tissues, depending on the positron emitting isotope chosen and the molecule (if any) to which it is attached. Coregistration and image fusion techniques allow for powerful combinations of functional images from PET and structural images, usually from CT, which can give precise information on the anatomic location of structures seen on PET (Hutton et al. 2002). Fused CT/PET images are proving to be superior to separate CT or PET images in cancer staging (Townsend and Beyer 2002). PET scanning is becoming an essential tool for planning radical radiotherapy for lung cancer, which should ideally be based on the most accurate available estimate of the true extent of gross disease. PET has the potential to exclude patients from radical radiotherapy who cannot benefi t from it because they have metastatic disease. Evidence supports the use of PET in radiotherapy treatment planning (Erdi et al. 2002; Kiffer et al. 1998; Mah et al. 2002). By more accurately conforming the planning target volume to gross tumour volume, the risk of a geographic miss can be minimised, and in some cases the unnecessary irradiation of normal tissues can be reduced (Mah et al. 2002; Schmucking et al. 2003). Preliminary data indicate that the new combined PET/CT scanner may provide the most effi cient and accurate means of integrating structural and molecular information into the treatment planning paradigm (Ciernik et al. 2003). Most published studies of PET in lung cancer have focused on the use of 18F-fl uorodeoxyglucose (FDG), a glucose analogue that is taken up and trapped by tumour cells in most non-small cell lung cancers (NSCLC). The positrons emitted by the 18F atom travel a short distance before they encounter an electron and undergo annihilation with the emission of a pair of photons in opposite directions. When the annihilations of millions of positrons are detected in a PET scanner, a detailed three-dimensional image of the distribution of FDG in normal and tumour tissue can be produced. Although limited data are available for small cell lung cancer that is well-imaged by FDGPET (Pandit et al. 2003), the bulk of the literature on the value of PET scanning in lung cancer relates to NSCLC. The role of PET in evaluating patients with known or suspected lung cancer will be reviewed in this chapter, with particular emphasis on information of value for managing patients who are planned to receive radical radiotherapy. CONTENTS