Hopkins investigators have found that a combination of positron emission tomography (PET) and computed tomography (CT) detects cancer spread better than PET alone. In a study to be presented at the Radiological Society of North America (Abstract #1458, 10:57 AM, CT, Thursday, December 5, Room S502AB), researchers reported that overall, PET-CT improves the ability to distinguish cancerous from normal tissue and locate metastases, where they have spread. The study used a scanner that fuses CT technology, which provides anatomical detail, with PET images, which detects metabolic activity of tumors.
Ten PET and 33 PET-CT scans were performed on 28 patients with ovarian cancer suspected to have spread to the abdominal cavity. There were three true positive and two true negative results with PET alone and 14 true positives and 10 true negatives with PET-CT. The PET scan alone produced two false positives, while PET-CT produced none. There were no false negatives with PET alone, and PET-CT had five. Combined PET-CT had a fairly high sensitivity rate, accurately diagnosing cancer 73.6 percent of the time (14 of 19), and PET alone was able to diagnose all three positive cancers.
“PET-CT was very specific, as it was able to distinguish cancer from non-cancer 100 percent of the time (10 of 10), while PET alone was specific for cancer only 50 percent of the time (two of four),” says Richard L. Wahl, M.D., the Henry N. Wagner Jr. professor of nuclear medicine and director of the division of nuclear medicine at Johns Hopkins. Routine contrast-enhanced CT was able to find disease in three of the five false negatives produced by PET-CT.
“The CT portion of combined PET-CT scanners is very helpful at locating disease, but it could miss some lesions that can be found with contrast-enhanced CT,” says Elliot K. Fishman, M.D., professor of radiology and oncology and director of diagnostic imaging and body CT for the Kimmel Cancer Center at Johns Hopkins.
The researchers caution that this study is in a limited number of patients and additional research is necessary to determine the value of combined PET/CT over PET alone and over CT. “Nonetheless, our results are very promising and PET/CT is being used more often for patients with suspected recurrent ovarian cancer,” says Wahl.
A second study by Wahl and Fishman being presented at the meeting (Abstract #740) shows how whole body CT provides a 19 percent improvement to combined PET-CT in detecting colorectal cancer recurrence.
Johns Hopkins was the first U.S. hospital to install a commercial combination PET-CT scanner for use with patients in a clinical setting. In addition to ovarian and colon cancer, the scanner is being used to detect a variety of cancers including breast, melanoma, and lung cancer.
In addition to Wahl and Fishman, other participants in this research were first author, Harpreet Pannu, M.D., Christian Cohade, M.D., Robert Bristow, M.D., and Fredrick Montz, M.D.