PET/CT proves superior in more ways than one

PET/CT is significantly more accurate than CT alone, PET alone, and side-by-side CT and PET for evaluating the TNM stage of various malignant diseases. This diagnostic advantage translates into treatment plan changes in a substantial number of patients, according to Dr. Gerald Antoch and colleagues at University Hospital Essen in Germany.

Researchers viewed scans from 260 consecutive patients (167 female) with different oncologic diseases who had undergone FDG-PET/CT for tumor staging. One hundred twelve patients were imaged for primary tumor staging and 148 for suspected recurrent disease.

The majority of patients had malignant non-small cell lung carcinoma, followed by head and neck tumors, gastrointestinal tumors, and others. The researchers performed PET/CT with an axial field-of-view from head to upper thigh, using intravenous contrast CT for diagnostic data.

Two nuclear medicine specialists viewed the PET-alone images. They evaluated the images first qualitatively by the areas of increased glucose metabolism, then quantitatively by the standard uptake value.

An SUV cutoff value of 2.5 for malignancy was used for all organs except the liver, for which it was 3.5. The difference in cutoff values was based on an analysis of the literature that showed generally higher FDG uptake in the liver than in the rest of the body organs, Antoch said.

Two radiologists examined the CT images and determined whether lymph nodes were metastatic based on their size. Side-by-side images were evaluated by radiologists and nuclear medicine specialists on two different screens: CT on the right screen, PET on the left. The images were purposely misregistered to ensure a degree of objectivity.

The same radiologists and nuclear medicine specialists reviewed the fused images one month after the side-by-side image analysis. Increased glucose metabolism was again used to determine pathology.

The researchers performed a separate analysis for the T-, N-, and M-stages and also determined the impact of PET/CT on patient management.

Histopathology was the standard of reference for 77 patients for the T-stage, 72 patients for the N-stage, and 57 patients for the M-stage. For all other patients, clinical follow-up served as the standard of reference.

Fused PET/CT proved significantly more accurate in assessing the overall TNM stage compared with CT alone, PET alone, and side-by-side CT plus PET.

Of all 260 patients, 84 % were correctly staged with PET/CT, 76% with side-by-side CT plus PET, 64% with PET alone, and 63 % with CT alone.

Sensitivities and specificities for characterization of the N-stage were 92% and 93% for PET/CT, 88% and 89% for CT plus PET, 85% and 88% for PET, and 64% and 83% for CT.

Sensitivities and specificities for assessment of the M-stage were 94% and 97% with PET/CT, 92% and 96% with CT plus PET, 78% and 99% with PET, and 82% and 95% with CT.

"The most important point is whether PET/CT had an impact on patient management," Antoch said. "Does it change patient therapy from palliative to curative, from curative to palliative? Or does it change the surgical approach from extended surgery to limited surgery?"

Combined PET/CT affected the treatment plan for 17% of patients compared with PET alone, for 15% of patients compared with CT alone, and for 6% of patients compared with side-by-side CT plus PET.