PET/CT imaging of prostate cancer. Coronal attenuation-corrected PET shows moderately hypermetabolic foci along the left iliac nodal basin. Axial pelvic CT shows a small lymph node at the aortic bifurcation corresponding to the upper hypermetabolic lesion on PET. (Provided by H. Jadvar)

Thursday, 12/5/02,4:47 PM PST
PET/CT proves its value in ovarian and prostate cancers
By Harold Abella

Combining PET with CT -- and in some cases with MRI -- provides a valuable clinical tool for detection and restaging of recurrent disease and metastases in patients with ovarian and prostate cancer. But the method is not without pitfalls, according to papers presented Thursday at the RSNA meeting.

In a study of 51 women who had undergone treatment for ovarian cancer, researchers from Seoul, South Korea investigated whether fluorine-18 FDG-PET in combination with CT or MRI could find hidden tumors in these patients. They compared the diagnostic accuracy of PET, combined PET with CT or MRI, measurement of serum CA-125 level, and physical examination.

The group found that PET combined with anatomic imaging was better than serum CA-125 level and physical examination for detection of residual tumors. Hybrid imaging correctly identified tumors in 21 of 25 patients, with sensitivity and specificity of 84% and 76.9%, respectively.

According to the investigators, an abnormal finding on FDG-PET with CT or MRI is a strong indicator of residual or recurrent tumor, even in a patient with a normal serum CA-125 level. But although hybrid imaging offers outstanding sensitivity, it could also compromise specificity, they said.

In a study of 28 patients, researchers from Johns Hopkins University compared sensitivity and specificity for both PET and PET/CT for the detection of peritoneal metastases from ovarian cancer. These metastases are often small and may be completely overlooked on CT.

The group found fused PET/CT scans highly accurate and more specific than PET alone in detecting peritoneal metastases.

"The CT portion of the PET/CT scan is appropriate for localization, but it is limited for finding peritoneal lesions as a separate modality," said Dr. Harpreet Pannu, a radiologist at Johns Hopkins.

A University of Southern California study of nine men compared PET with CT and MRI for detection of suspected recurrent and metastatic prostate cancer. The researchers found that PET could identify suspicious hypermetabolic pelvic lymph nodes in cases where CT scans were negative, said Dr. Hossein Jadvar, an assistant professor of radiology at USC.

PET results correlated with CT and MRI findings in most cases. Overall results, however, indicated that FDG-PET was limited in the detection of osseous bone metastases, Jadvar said.