Computed tomography (CT) and positron-emission tomography (PET) commonly are used in the initial staging of lung cancer and other malignancies. While CT can provide excellent detail on the size and location of tumor masses and adjacent lymph nodes, it sometimes cannot differentiate between benign and malignant tissue. PET uses radio-tracers to mark areas of increased uptake in malignant tissue but has limited spatial resolution. Side-by-side visual comparison of CT and PET scans, although often employed in cancer staging, is laborious and may be inexact. A recent innovation in tumor imaging is the use of integrated PET-CT scanners that provide precisely overlayed images. Lardinois and colleagues report on the comparative diagnostic accuracy of separate and combined CT and PET imaging for the staging of non–small-cell lung cancer.

The authors studied 50 consecutive patients with suspected or proven lung cancer who were referred for surgery at a university hospital. Conventional staging was done with standard modalities, including bronchoscopy and blood testing. Each patient underwent whole-body imaging in a combined PET-CT scanner. Separate PET and CT images were produced, as well as a combined overlay. One patient was excluded when biopsy results indicated lymphoma, not lung cancer. Mediastinal lymph node dissection was performed in 35 patients. Those with widely metastatic disease or no nodes larger than 5 mm did not have surgical lymph node exploration.

When compared with visual correlation of separate PET and CT scans, combined PET-CT images provided additional information that changed clinical management in 41 percent of patients. Among the additional findings seen with combined imaging were otherwise undetected local and wide metastatic tumor spread, differentiation of malignant tissue from adjacent lung inflammation and atelectasis, and more precise location of lymph node positions.

Integrated PET-CT was the most accurate preoperative method for disease classification, correctly staging the disease compared with the postsurgical diagnosis in 88 percent of cases. PET alone correctly classified 40 percent, CT alone 58 percent, and visually correlated separate PET and CT scans were correct in 65 percent of patients. Of the nine patients incorrectly classified by visual correlation of separate scans, eight were correctly staged by the combined PET-CT images.

The authors conclude that integrated PET-CT improved the diagnostic accuracy of non–small-cell lung cancer staging when compared with separate scans.