Chest
Volume 128, Issue 4, October 2005, Pages 2490-2496
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Clinical Investigations
Clinical Prediction Model To Characterize Pulmonary Nodules: Validation and Added Value of 18 F-Fluorodeoxyglucose Positron Emission Tomography

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Background

The added value of 18 F-fluorodeoxyglucose (FDG) positron emission tomography (PET) scanning as a function of pretest risk assessment in indeterminate pulmonary nodules is still unclear.

Objective

To obtain an external validation of the prediction model according to Swensen and colleagues, and to quantify the potential added value of FDG-PET scanning as a function of its operating characteristics in relation to this prediction model, in a population of patients with radiologically indeterminate pulmonary nodules.

Design, setting, and patients

Between August 1997 and March 2001, all patients with an indeterminate solitary pulmonary nodule who had been referred for FDG-PET scanning were retrospectively identified from the database of the PET center at the VU University Medical Center.

Results

One hundred six patients were eligible for the study, and 61 patients (57%) proved to have malignant nodules. The goodness-of-fit statistic for the model (according to Swensen) indicated that the observed proportion of malignancies did not differ from the predicted proportion (p = 0.46). PET scan results, which were classified using the 4-point intensity scale reading, yielded an area under the evaluated receiver operating characteristic curve of 0.88 (95% confidence interval [CI], 0.77 to 0.91). The estimated difference of 0.095 (95% CI, −0.003 to 0.193) between the PET scan results classified using the 4-point intensity scale reading and the area under the curve (AUC) from the Swensen prediction was not significant (p = 0.058). The PET scan results, when added to the predicted probability calculated by the Swensen model, improves the AUC by 13.6% (95% CI, 6 to 21; p = 0.0003).

Conclusion

The clinical prediction model of Swensen et al was proven to have external validity. However, especially in the lower range of its estimates, the model may underestimate the actual probability of malignancy. The combination of visually read FDG-PET scans and pretest factors appears to yield the best accuracy.

Section snippets

Materials and Methods

Between August 1997 and March 2001, all patients with an indeterminate SPN, which had been detected during normal clinical work in both university and community hospital settings, who had been referred for FDG-PET scanning were retrospectively identified from the database of the PET center at the VU University Medical Centre. In our database, the characteristics of all patients are registered using a modified version of the American College of Radiology Index for Radiologic Diagnoses.

An

Results

In total, 106 eligible patients were identified, of whom 61 (57.5%) proved to have malignant nodules. Referring physicians were pulmonologists from university hospitals (n = 25) and community hospitals (n = 81). Fifty-eight percent of the patients were men, and their mean age was 64 years (age range, 32 to 85 years) [Table 1]. The diagnosis of malignancy was based on histopathologic results in 55 patients and on radiologic growth of the lesion in 6 patients. The diagnosis of a benign lesion was

Discussion

In 2003, a comprehensive cost-effectiveness decision analysis was published,1 which included the full spectrum of diagnostic and therapeutic options for SPNs. The first stratification of this analysis was based on the result of a clinical risk assessment as provided by a previously developed multivariate logistic regression model.2 It was recognized that this model, which was developed in a North American population with pulmonary nodules discovered between 1984 and 1986 and a prevalence of

Conclusion

The clinical prediction model of Swensen et al2 has been proven to have external validity. However, especially in the lower range of its estimates, the model may underestimate the actual probability of malignancy. The visual analysis of FDG-PET scans is a robust and accurate method in radiologically indeterminate SPNs. The combination of visually read FDG-PET scans and pretest factors appears to yield the best accuracy. These results can help to adjust the diagnostic workup in individual

ACKNOWLEDGMENT

We thank V. Bongers, MD; R.A.M.J. Claessens, MD; M.A.L. Edelbroek, MD; D.A.K.C.J.M. Huysmans, MD; R.A. Valdés Olmos, MD; D.E.A. Zanin, MD; and A. Zwijnenburg, MD; who performed a visual analysis of FDG-PET scans using intensity scales to assess the interobserver correlation.

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