PET, Lymphoscintigraphy Expanding Into the Clinic

LOS ANGELES—“PET has arrived!” Edward Coleman, MD, said at a press conference held during the 46th annual meeting of the Society of Nuclear Medicine. Dr. Coleman, professor of radiology and director of the Nuclear Medicine Division, Duke University Medical Center, noted that “PET has expanded tremendously into the clinical environment.” He attributes this to the development of fluorodeoxyglucose (FDG) PET imaging and PET’s growing applications in oncology.

According to Dr. Coleman, there were about 50 US centers offering PET 2 to 3 years ago, whereas today there are more than 300. Furthermore, the number of patients having PET scans has doubled in the last 2 years, from 25,000 to almost 50,000 in 1998, and this number is rapidly increasing.

 “PET has proved to be accurate and cost effective in diagnosing the most common and deadly cancers, and is now available to more patients because the Health Care Financing Administration (HCFA) and other third-party payers are paying for additional indications,” he said. On July 1, 1999, HCFA added three new indications for FDG-PET imaging: evaluation of recurrent colorectal cancer, staging of lymphoma, and detection of recurrent melanoma.

Dr. Coleman believes that PET is becoming the “gold standard” for diagnosing cancer and other illnesses. He said that PET is more accurate not only diagnostically but also in determining the distribution of the disease. “Clinical PET finds cancers missed by other diagnostic tools,” Dr. Coleman said. “If you more accurately diagnose a patient, you can better treat that patient, and you would certainly expect better survival.”

Finding the Sentinel Node

Lymphoscintigraphy is another imaging procedure “not exactly brand new to nuclear medicine” that is receiving increased attention as physicians learn to use it to refine and direct cancer therapy, Robert Henkin MD, professor of radiology, Loyola University Medical Center, Chicago, said at the press conference.

 “Lymphoscintigraphy is growing tremendously right now. Two to 3 years ago at our institution, we were doing approximately one a month, and now we do up to two or three a day,” Dr. Henkin said. “The best treatment for involved lymph nodes is surgical removal. But you’ve got to be able to know which patients need to have the nodes removed, and that’s the goal of this technique.”

Lymphoscintigraphy maps the drainage of the lymph nodes from the region of the tumor, he said. A small amount of radiotracer is injected around the tumor; the first lymph node that can be detected with a gamma camera and a hand-held probe is most often the sentinel node.

“Traditionally, the surgeon has not known which lymph node is the correct node to be removed for biopsy,” Dr. Henkin said. “As a result, the surgeon removes all the lymph nodes, the complications of which are not trivial.”

He cited a Dutch study in which predicting the location of the first draining node based on anatomy alone produced an error rate of about 20%. “That means that 20% of patients who do not undergo lymphoscintigraphy may be under- or overtreated,” he said.