PET tops CT for early characterization of malignant lung nodules

April 11, 2008

A large multicenter trial rates FDG-PET as more reliable than CT for the detection of malignant solitary pulmonary nodules. The findings suggest, however, that a combined rather than single-modality approach may lead to earlier treatment and help avoid invasive procedures.

A large multicenter trial rates FDG-PET as more reliable than CT for the detection of malignant solitary pulmonary nodules. The findings suggest, however, that a combined rather than single-modality approach may lead to earlier treatment and help avoid invasive procedures.

The clinical literature notes that suspicious lung nodules appear frequently as incidental findings on chest radiography or CT. These cases are usually followed up with PET or CT to characterize lesions as benign or malignant. Most studies done to evaluate CT's accuracy in this setting, however, have been performed with outdated technology, while PET studies have typically included small patient cohorts of questionable statistical merit.

The latest study, a collaborative effort of 10 VA hospitals in seven states, addressed previous research limitations. It is the largest and most rigorous evaluation of PET in patients with solitary pulmonary nodules (SPNs) and one of only a few studies to compare the accuracy of PET and CT for this indication, said principal investigator Dr. James W. Fletcher, a professor of radiology at Indiana University School of Medicine in Indianapolis.

From January 1999 to June 2001, Fletcher and colleagues prospectively enrolled 344 patients with a recent diagnosis of SPN who had not yet been treated for the condition. All patients underwent fluorine-18 FDG-PET and CT scanning. A panel of PET and CT experts compared imaging results and correlated them with biopsies from 184 of these patients and two-year follow-up data from 160 of them.

The investigators found that both PET and CT could predict benign diagnoses. Accurate results were more frequent with PET, however, which correctly classified 58% of benign nodules incorrectly characterized as malignant on CT. Researchers also found that PET results interpreted as definitely malignant according to pre-established SPN rating criteria were 10 times more likely to yield a malignant final diagnosis than a benign one.

The researchers published their results in The Journal of Nuclear Medicine (2008;49:179-185).

The average size of nodules was 16 mm, with a prevalence of malignant lesions in 53% of cases. Of these, 35% were adenocarcinomas, 30% squamous cell carcinomas, and 20% other non-small cell lung cancers. Nodules from metastatic disease to the lung represented less than 10% of the total. Less than 2% were bronchoalveolar carcinomas.

"FDG-PET can accurately characterize malignant nodules early, when they are stage I lung tumors. This facilitates aggressive treatment when patient survival rates are much higher," Fletcher told Diagnostic Imaging.

Findings also confirm that both FDG-PET and CT can independently identify benign nodules with a high sensitivity and low false-negative rate. This capability would facilitate a more conservative "watch and wait" strategy in many patients and could avoid unnecessary invasive procedures such as biopsy or surgery, Fletcher said.

Nodules larger than 3 cm have a higher likelihood of being malignant, while nodules below 7 mm are generally poorly characterized by PET, according to Fletcher. On the other hand, only 1% of the nodules were classified as indeterminate by PET, whereas almost one-fourth of CT findings were interpreted as indeterminate and often associated with further invasive assessment.

Here is where PET/CT systems could play an important role, Fletcher said.

"(The study) further advances our understanding of the role of FDG-PET and CT as well as identifying some of the limitations of CT performed in an independent manner," he said. "It is possible to extrapolate these findings to the likely performance of dual-modality PET/CT systems that can take advantage of the performance characteristics of both imaging modalities."

For more information from the Diagnostic Imaging archives:

PET alters management for one in three patients

Whole-body cancer staging requires frequent follow-up in some patients

Innovation drives growth of hybrid imaging

Hybrid imaging proves more sensitive and specific than solo scanners