PET/CT is Superior to 3T MRI for Whole-Body Primary Tumor Staging

Determining how far a patient's cancer has metastasized is crucial in planning and optimizing treatment. A variety of imaging techniques now provide essential tools for staging primary tumors, including positron emission tomography (PET), compute tomography (CT), and magnetic resonance imaging (MRI), but a new comparative study revealed that fused whole-body PET/CT to be considerably more accurate than whole-body MRI--even at 3 Tesla--for primary tumor staging.

Between November 2002 and January 2008, a group of Italian investigators evaluated the effectiveness of whole-body FDG-PET/CT images versus images from CT alone, CT+PET images viewed side-by-side, and whole-body 3-Tesla MR images. They presented the findings of their study in March 2008 at the 2008 European Congress of Radiology (ECR), held in Vienna, Austria. "The aim of the study was to determine the potential benefits concerning patient management when staging primary tumors--that is, the diagnostic advantages and impact on treatment,” said Dr. Stefano Mancino, from Tor Vergata University (Rome, Italy).

The patients in the study had a range of cancers, including five cases of breast cancer, four lung cancers, three liver carcinomas, two melanomas, and six lymphomas. The researchers obtained CT and PET/CT images of the patients using a PET/CT scanner (Discovery ST PET/CT system, developed by GE Healthcare; Chalfont St. Giles, UK) with an acquisition time of approximately 30 minutes, while the MRI images were acquired on a 3-Tesla machine (Achieva 3.0T MRI system, developed by Philips Healthcare; Best, The Netherlands) using a body coil and an unlimited field-of-view.

Results showed a superior diagnostic performance from fused PET/CT imaging, which was significantly more accurate in assessing overall tumor, node, metastases (TNM) staging versus standalone CT (p < 0.05), side-by-side CT+PET (p < 0.05), and whole-body MRI.

Of the 20 patients in the study, PET/CT accurately staged 16 (80%), side-by-side CT+PET was accurate in 14 (70%) cases, and CT imaging alone identified 13 (65%) cancers, while 3-Tesla MRI correctly staged tumors in 12 (60%) patients. The distinct diagnostic advantages as highlighted in this study were translated into changes and improvements in the clinical management of several patients, according to Dr. Mancino.

There was discordance between PET/CT and MRI results when identifying small lesions in the left liver segment and depicting metastases. PET/CT and side-by-side CT+PET were more sensitive in depicting small bone lesions and pulmonary lesions than CT alone, Dr. Mancino noted.

In specifically assessing metastases (M staging), any differences in the relative performance of PET/CT and CT+PET viewed side by side were not statistically significant, according to Dr. Mancino. He, however, recognized whole-body MRI to be an effective tool for staging cancer patients but added that based on his team's experience, "it cannot reach the accuracy of fused FDG-PET/CT images. Whole-body fused PET/CT is significantly more accurate than CT alone and CT+PET side by side in staging malignant disease,” he concluded.

In related research, Dr. Till Heusner, from the University of Duisburg-Essen (Germany), compared whole-body MRI and whole-body FDG-PET/CT in detecting bone metastases at initial diagnosis in patients with malignant melanoma and nonsmall cell lung cancer (NSCLC). Both imaging procedures were performed within a 14-day period, with a mean interval of 0.6 days. Differences between the imaging procedures were tested for significance using McNemar's test (p < 0.05).

Based on the standard reference that three patients with malignant melanoma and eight with NSCLC had bone metastases (of the total 109-patient study group), the study's revealed that FDG-PET/CT correctly detected bone metastases in five patients, whereas MRI did the same in seven patients.

Each of the five metastases discovered using PET/CT imaging were in the NSCLC group; MRI also found five in this group, and two in the melanoma group. However, both imaging modalities had false-positive results: MRI produced six false positives, whereas PET/CT produced one false-positive result.

While he reported that the results from this relatively small study would benefit from validation in a larger study, Dr. Heusner concluded that whole-body FDG-PET/CT and whole-body MRI were similarly accurate in assessing patients at initial diagnosis of malignant melanoma and NSCLC.


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Tor Vergata University
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