Inner Visions
New technology takes clinicians and researchers on a "fantastic
voyage" throughout the body to analyze cancer and other disorders.
Initially, it was the X-ray that had the distinction of being the
eyes of the physician, a medical sentinel probing the body's interior
for bone fractures and diseased organs. As time and technology advanced,
more sophisticated equipment assumed that role. Now researchers
are combining two modern systems - positron emission tomography
and computed tomography - to give physicians the closest thing to
20/20 vision available.
The Indiana University School of Medicine was one of the first
three institutions nationally to install a PET/CT fusion-imaging
system. "The state-of-the-art diagnostic scanner gives us a
more comprehensive look at tumor growth for the staging of cancers,
location of tumors, and the effectiveness of therapeutic agents
and surgery," says Gary Hutchins, PhD, vice chairman of research,
Department of Radiology.
"Within the next two or three years, I think PET/CT will be
a first-line procedure in the management of patients with cancer,"
adds James Fletcher, MD, director of nuclear medicine and of the
Clinical PET Imaging Center.
PET scanning has been available for clinical use since 1990 but
wasn't routinely used for cancer management until it received Medicare
coverage for lung cancer in January 1998. Its use for diagnosis,
initial cancer staging and evaluation of response to therapy has
expanded greatly since that time. It also is an effective tool for
physicians wanting to gauge the viability of tissue in the heart
and to study brain metabolism in tumors and disorders such as Alzheimer
disease.
PET's biggest limitation is poor spatial resolution, Dr. Hutchins
observes. On the other hand, he adds, CT images excel at showing
spatial context.
As a member of the IU Cancer Center, Dr. Hutchins uses PET and now
PET/CT in research looking at disease physiology in animal models,
including a current study looking at the rate at which bone cancer
metastasizes to the lung, and a series of studies using mice to
find a genetic marker for breast cancer. The dual imaging system
has brought a new dimension, literally, to Dr. Hutchins' bone cancer
research.
"What PET offers is an understanding of disease from a metabolic
or biochemical point of view," explains Dr. Fletcher. "Sometimes
the first sign of cancer is a metabolic change."
PET takes advantage of the facts that cells use glucose for energy,
and that rapidly growing cells such as tumors or malignancies burn
more energy. The patient is given a radioactive labeled form of
glucose known as 18F-fluorodeoxy glucose or FDG, which is taken
up during cell metabolism. The scan reveals the metabolic rate of
glucose utilization in the tissue, with fast-growing areas showing
up as "hot spots" on the PET scan. What PET doesn't show
is precise location; that's where CT offers an advantage.
Used alone, CT measures anatomy and morphologic changes associated
with disease. A contrast agent is injected or ingested that allows
radiologists to see concentrations of blood volume to determine
the existence of tumors or masses of abnormal tissue. Though CT
slices reveal anatomical structure and abnormalities, they are not
as accurate as physicians would like.
"In certain common cancers, CT has been wrong in over half
the instances where it indicated the patient's cancer was operable,"
says Dr. Fletcher. "CT also often can miss metastatic sites."
However, combining the two technologies overcomes their individual
limitations, letting physicians better identify and localize abnormalities.
PET/CT fusion-imaging helped IU physicians identify the presence
of a tumor inside a major vein in the chest of a 35-year-old man
who was initially treated for testicular cancer in 1987.
In late 2001 - not long after the new imaging technology was in
place - the patient returned to IU complaining of swelling in his
face and neck. A chest X-ray revealed a large mass inside his chest,
and he underwent surgery and chemotherapy. His serum marker for
tumor returned to normal until a follow-up visit last April when
his serum marker levels were found to be increasing. A CT scan of
the chest showed nothing abnormal. But PET/CT scanning revealed
a tumor inside the superior vena cava, a condition readily treatable
by surgery.
"The role that PET/CT played was very critical since it clearly
identified the presence of a treatable recurrent tumor," says
Dr. Fletcher. "The PET component was able to easily identify
the presence of an abnormality that had been missed by a prior routine
CT exam. The CT component helped to localize the abnormality to
the vein in the chest, a very unusual location for a tumor. We now
can find tumor sites not seen through PET or CT alone."
PET/CT gives physicians a better look at disease sites to determine
if surgery is an option or if the cancer has spread beyond the point
where surgery is recommended.
The combined imaging also offers physicians an early opportunity
to measure the effectiveness of chemotherapy. If the drug is not
working, the regimen can be changed.
IU's Siemens Biograph Pet/CT system was installed in December 2001
and physicians already have ascertained its value to patient care.
The Department of Radiology is in the process of purchasing a second
PET/CT at a cost of nearly $2.5 million.
With a price tag of nearly $2,800 per procedure, it is crucial
for insurance to recognize the effectiveness of the PET/CT over
the use of the two systems. Dr. Fletcher is working to make that
happen. Currently he is providing physicians with separate PET and
CT data to document how the information influences medical treatment
decisions. Preliminary results indicate PET/CT images make a substantial
difference in clinical decision-making, he says. He notes that an
important part of this process will be to develop new medical coding
for insurance companies.
"By demonstrating that PET/CT adds value to patient care,
insurance reimbursements will be more favorable and the government
will take a more favorable view of funding research," Dr. Fletcher
says.
|
