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Whole-body PET/CT outperforms MRI when determining tumor stage

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A 66-year-old male with bronchial carcinoma of the right lower pulmonary lobe. MRI demonstrates mediastinal lymph node, which was not pathologically enlarged. The PET/CT data sets, however, reveal focally increased glucose metabolism within the mediastinal lymph node. Mediastinal metastasis was suspected based on the PET/CT scan. Histology later proved mediastinal lymph node involvement (N2-disease). (Gerald Antoch, MD)

A new study suggests whole-body PET/CT imaging may be more useful than whole-body MRI for determining the extent a tumor has spread, according to an article in a recent issue of the Journal of the American Medical Association (JAMA).

In malignant diseases, therapeutic options as well as patients' prognoses strongly depend on the tumor stage. Thus, accurate tumor staging encompassing the entire body is essential. MRI and PET/CT provide means for whole-body tumor staging in a single session. In contrast to MRI, which is mainly focused on the assessment of morphological (structural) characteristics of tissue, FDG-PET provides functional information on tumor metabolism. The functional data available in whole-body scans complement morphological imaging for staging different malignancies.

Gerald Antoch, MD, of the University Hospital Essen, Germany, and colleagues conducted a study to determine the staging accuracies of whole-body PET/CT and whole-body MRI for different malignant diseases and to compare these two new imaging tools.

The study included 98 patients (mean age 58 years; range, 27 to 94 years) with various cancers who underwent back-to-back whole-body PET/CT and whole-body MRI for tumor staging. The study was conducted at a university hospital from December 2001 through October 2002 and had a mean follow-up of 273 days (range, 75 to 515 days). Two different teams evaluated the images. The diagnostic accuracies of both imaging procedures were compared.

The researchers found that of the 98 patients, the overall primary tumor, regional lymph nodes and distant metastasis (TNM) stage were correctly determined in 75 patients with PET/CT (77 percent) and in 53 patients with MRI (54 percent). "Compared with MRI, PET/CT had a direct impact on patient management in 12 patients. Results from MRI changed the therapy regimen in two patients compared with PET/CT. Separate assessment of tumor stage (with pathological verification) in 46 patients revealed PET/CT to be accurate in 37 patients (80 percent) and MRI to be accurate in 24 patients (52 percent). Of 98 patients, lymph node stage was correctly determined in 91 patients with PET/CT (93 percent) and in 77 patients with MRI (79 percent). Both imaging procedures showed a similar performance in detecting distant metastases," the authors write.

"The most crucial aspect of clinical tumor staging relates to the staging impact on patient management. Compared with whole-body MRI, the therapy regimen was altered in a substantially larger number of patients when staging analysis was based on the PET/CT data. Therefore, FDG-PET/CT can be recommended as a first-line tool for whole-body tumor staging of different oncological diseases," the researchers conclude.

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— Journal of the American Medical Association