At this time, however, Medicaid, Medicare and many private insurers specify CT (computed tomography) for diagnosing and monitoring this cancer. The researchers are hoping to encourage a change in that standard report with their recent comparison of the two methods. The results suggest that the use of PET, or positron emission tomography, would make diagnosis of vaginal cancer much more accurate and allow better selection of treatment, according to study author Perry W. Grigsby, M.D., professor of radiation oncology and radiology.

"When you're evaluating lymph nodes for cancer using CT, the node has to be at least a centimeter for it to be considered abnormal. But PET scans can detect much smaller nodes that have cancerous cells", says Grigsby, who sees patients at the Siteman Cancer Center and is affiliated with Barnes-Jewish and St. Louis Children's Hospitals.

PET scans are effective for this purpose because they use a different detection method than CT scans. CT scans obtain cross-sectional views of the body by detecting the amount of X-rays that pass through the body's tissues. Small tumours can easily escape detection.

On the other hand, PET scans detect radioactivity that emanates directly from a tumour after a patient has received a dose of radioactive glucose, which accumulates in tumours. Even tiny tumours will collect enough "hot" glucose to show up on the PET scan.

"It is very important to know at the time of diagnosis, for both cervical and vaginal cancer, not only what the patient has in the pelvis, but where the tumour has spread," Grigsby says. "That will absolutely determine the kind of treatment."; Source: Washington University School of Medicine