PET outperforms CT for the detection of lung nodules

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PET accurately identified malignant or benign solitary pulmonary nodules far more often than CT, according to a multi-institutional study in the February issue of the Journal of Nuclear Medicine.

"CT and PET have been widely used to characterize SPNs as benign or malignant," wrote lead author James W. Fletcher, professor of radiology at Indiana University School of Medicine in Indianapolis. "Almost all previous studies examining the accuracy of CT for characterizing lung nodules, however, were performed more than 15 years ago with outdated technology and methods, and previous PET studies were limited by small sample sizes," he noted.

Fletcher and colleagues recruited 532 participants with SPNs newly diagnosed on radiography and untreated between January 1999 and June 2001. All patients underwent 18F-FDG PET and CT, and the SPNs were 7–30 mm. SPN tissue diagnosis or a 2-year follow-up established the final diagnosis, according to the investigators.

The researchers reported that a definitive diagnosis was established for 344 participants; the prevalence of malignancy was 53 percent; and the average size was 16 mm. The authors also wrote that likelihood ratios (LRs) for PET and CT results for combined ratings of either definitely benign (33 percent and 9 percent of patients, respectively), or probably benign (27 percent and 12 percent) were 0.10 and 0.11, respectively.

The LRs for PET and CT results for combined ratings of indeterminate (1 percent and 25 percent), probably malignant (21 percent and 39 percent), or definitely malignant (35 percent and 15 percent) were 5.18 and 1.61, respectively, according to the researchers.

Fletcher and colleagues found that definitely and probably benign results on PET and CT strongly predict benign SPN, but, such results were three times more common with PET. They also concluded that the malignant final diagnosis was approximately 10 times more likely than a benign final diagnosis in participants with PET results rated definitely malignant.

"In patients with an untreated and undiagnosed SPN between 7–30 mm, PET provides better identification of malignant nodules that require a more aggressive treatment approach," Fletcher said. "PET in combination with CT can also provide good identification of those nodules that are most likely to be benign, suggesting that a 'watch and wait' strategy can be adopted in lieu of unnecessary invasive-and expensive-procedures such as needle biopsy or surgery," he added.