has been questioned.11 Therefore CT assessment has been estimated to incorrectly over stage
or under stage T and N status in 40% of cases. Therefore some form of surgical verification is
needed to confirm the CT scan. The value of the mediastinoscopy as a further staging
procedure is widely accepted mainly due to its high specificity in detecting nodal involvement.
However, it does have limitations as it can not access all lymph nodes (reducing its sensitivity).
Furthermore, it also carries a small mortality risk.12 In the last 15 years positron emission
tomography (PET) has promised to improve the staging in NSCLC. There is a large literature
supporting PET as a useful tool in detecting distant metastasis and it is generally considered
that PET is more accurate than CT alone in identifying mediastinal lymph node (N2/N3)
invasion.13
What is FDG-PET?
PET is an imaging method that allows the metabolic rate of normal and disease tissue to
be compared using radiotracers, which other medical imaging techniques are unable to do.
Malignant tumours have a markedly accelerated metabolism, which can be visualised by 18F-
fluoro-2-dexy-D-glucose (FDG) due to a higher uptake of glucose in the tumour. Elevated
uptake of FDG has been demonstrated in all lung cancer cell types and this radiotracer is used
in most studies of lung cancer. The patient is administrated 350-500 megabecquerels (MBq) of
FDG with the data being acquired after an uptake interval of between 30 to 60 minutes. Whole
body imaging is used for screening and staging outside the limited primary field of view. False
positive results are reported and account for the lower specificity of FDG-PET relative to its
sensitivity. Reasons for false positives are mostly of an inflammatory nature. The high negative
predictive value of PET in mediastinal staging allows patients with a negative scan to
procedure to thoractomy without invasive mediastinal staging by mediastinoscopy. However it
will only be through the correct combination of CT, mediastinoscopy and PET procedures that
the most cost effective outcome to correctly stage NSCLC will be found.14
Some of the potential benefits of PET identified by the Bradbury et al study15 were to:
a) Increase the number of correct operations for N0/1 M0 patients and also to reduce
the number of missed operations within this group.
b) Avoid the resource cost of futile operations for which it does not offer a potential
cure. i.e N2/N3, M1 patients.
c) Avoid the mortality and morbidity of futile operations, especially the number of
‘open and shut” cases where the patients are opened up but they are inoperable and
are then referred to palliation.
d) Allow palliative care to be offered at an earlier stage for symptom control and more
appropriate care to be given.
e) Reduce the number of other diagnostic tests to be given.
11 Devaraj, A., G. J. Cook, et al. (2007). "PET/CT in non-small cell lung cancer staging-promises and problems."
Clinical Radiology 62(2), p. 99.
12 Clinical Practice Guidelines for the Prevention, Diagnosis of Lung Cancer. National Health and Medical
Research Council (2004) p.54.
13 Nguyen, V. H., S. Peloquin, et al. (2005). "Cost-effectiveness of positron emission tomography for the
management of potentially operable non-small cell lung cancer in Quebec" Canadian Respiratory Journal 12(1):
p.20.
14 Chiti, A., F. A. Schreiner, et al. (1999). "Nuclear medicine procedures in lung cancer." Eur J Nucl Med 26(5),
pp. 544-545.
15 Bradbury et al. Heakth Technology Board Scotland, Positron Emission Tomography (PET) Imaging in Cancer
Management” October 2002.