PET scans can detect twice the number of vaginal cancer and cancerous lymphnodes than CT scans. This was the finding from researchers at Washington University School of Medicine in St. Louis. An article has appeared in the July 1st issue of the 'International Journal of Radiation Oncology, Biology, Physics' and this may change the future gold standard for early detection of cancers of this region. According to study author Perry W. Grigsby, M.D., professor of radiation oncology and radiology, 'The results of this study 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'.
The vaginal cancer progresses in the known fashion, and if the staging of the tumour can be accurately predicted before treatment were to start the doctors can be sure of the modality of the treatment and where to target radiation treatment.
"In 1999, we began publishing papers showing that PET scans picked up more cancerous lymph nodes in patients with cervical cancer," Grigsby says.
PET scans and CT scans have different methods of detecting tumours. The CT scan obtains cross-sectional views of the body by detecting the amount of X-rays that pass through the body's tissues. CT scans can miss small tumors, whereas PET scans detect radioactivity that emanates directly from a tumor after a patient has received a dose of radioactive glucose, which accumulates in tumors. Hence even tiny tumors will collect enough "hot" glucose to show up on the PET scan.
"CT scans are useful in many cases, but they have a limit to their resolution," says Grigsby, who sees patients at the Siteman Cancer Center and is affiliated with Barnes-Jewish and St. Louis Children's Hospitals. "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."
Both vaginal and cervical cancers are caused by the presence of human papillomavirus. However cervical cancers are common but vaginal cancers account for only 1 percent of gynecological malignancies. According to Grigsby, if cervical cancer has not spread beyond its primary site, about 90 percent of patients will survive. The rate of survival drops to 70 percent if the cancer has spread to lymph nodes in the pelvis and even further to 30 to 40 percent if it has gone beyond the pelvic nodes. "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 tumor has spread," Grigsby says. "That will absolutely determine the kind of treatment."
Reference: Lamoreaux WT, Grigsby PW, Dehdashti F, Zoberi I, Powell MA, Gibb RK, Rader JS, Mutch DG, Siegel BA. FDG-PET evaluation of vaginal carcinoma. International Journal of Radiation Oncology, Biology, Physics. July 1, 2005;62(3):733-737,