have a mediastinoscopy or surgery in CT negative patients depending on the results of the
diagnosis this is based on evidenced cited by Dietlein on a survey of 529 thoracic surgeons.
The surgeons in the survey believed that in 58% of patients with CT negative results did not
require any further surgical staging and so went straight to surgery. 28 This distribution of
patients going to surgery or mediastinoscopy has therefore been adopted into the model here.
In CT positive patients, because the likelihood of mediastinal metastasis is high the
patients proceed to mediastinoscopy for further staging. Following mediastinoscopy patients in
both CT positive and CT negative will if negative proceed to surgery or if positive they will
proceed to a course of chemotherapy and radiotherapy in an effort to down stage the cancer. It
is assumed that patients with distant metastasis are not detected and patients may undergo
futile surgery or radiotherapy.
In the second strategy, the patients undergo a CWU but then receive a PET scan to
improve staging. Therefore, if patients’ results are positive on the FDG-PET then a
mediastinoscopy will be performed regardless of the lymph node size on CT results. If the
patients have a negative PET result then they would proceed straight to thoractomy. If PET
detects distant metastasis then a patients proceed to a course of palliative care.
Underlying Distribution of disease
The baseline population consisted of 62 year old man with whom NSCLC had been
confirmed and who was fit for surgery or non surgical treatment. Distant metastasis had not
been detected by conventional staging. The underlying distribution of the disease has been
taken from the literature.29
It is assumed that:
• 30% of patients have N2/3 disease.
• 10% have occult metastasis
• For N0/N1 disease, 23% have enlarged nodes
• For N2/3diseas, 60% have enlarged nodes
The underlying distribution of disease for PET candidates in the model given these parameters
is in table 2 below:
Table 2: HTBS distribution for NSCLC
|
N0/1, M0 |
N0/1, Ml |
N2/3, M0 |
N2/3, Ml | |
|
Normal lymph nodes |
48.4 |
5.4 |
10.7 |
1.2 |
|
Enlarged lymph |
14.6 |
1.6 |
16.3 |
1.8 |
This underlying distribution was questioned in the NICE study, suggesting that the rate
of distant metastasis was too low at 10% and that the constant rate for both N0/1 and N2/3
candidates was highly unrealistic. However, given the results of random clinical trials the rate
of metastasis does not seem too high, especially for N0/N1 patients where both models may be
28 Dietlein, M., K. Weber, et al. (2000). "Cost-effectiveness of FDG-PET for the management of potentially
operable non-small cell lung cancer: priority for a PET-based strategy after nodal-negative CT results." Eur J Nucl
Med 27(11): p.1600.
29 Dietlein, M., K. Weber, et al. (2000). & Bradbury et al. Health Technology Board Scotland, “Positron emission
tomography (PET) imaging in cancer management” October 2002.
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