Cancer Patients
Benefit from PET Scans through Penn Cancer Network
November / December 2002
PET is an advanced molecular imaging procedure that provides
a way to diagnose through the measurement of metabolic activity.
PET is a functional imaging technique: the images are derived
from the metabolism of the radiopharmaceuticals absorbed by
the tissue under study. As such, it complements anatomic-based
examinations such as x-ray, CT, and MRI. At times PET can
detect pathology before it becomes visible with CT or MRI
because metabolic changes often precede anatomic ones.
PET is a nuclear medicine procedure. The patient is injected
with a radiopharmaceutical, such as fluordeoxyglucose (FDG),
a radioactive glucose compound. Radiopharmaceuticals are
signal-emitting tracers when injected into the patient.
As the compounds are distributed throughout the body and
processed by the organ being targeted for imaging, the PET
scanner detects the FDG accumulated in glucose-avid organs
or tissues and creates images that are displayed on a video
monitor.
The signals detected by the camera are processed
by a computer to create images that display the distribution
of metabolic activity as a tomographic image similar to
the way an MRI machine will display images. Because cancer
cells have a higher metabolic rate than surrounding cells,
they absorb more of the tracer and will show up distinctly
on the image.
"Better than any other single radiologic technique, PET allows
us to make an earlier diagnosis, stage the cancer, check for
recurrences and assess the effectiveness of chemotherapy.
This information also enables us to select the most appropriate
treatment modality which may include surgery, radiation, and
chemotherapy or a combination for the most effective management
of the patient," says Abass
Alavi, MD, chief of Nuclear Medicine and director of
the Penn PET Center physician team.
"By receiving the preferred treatment there is an better
chance for improved results at an appropriate risk to the
patient. In some instances the PET scan can provide information
in one exam that might require multiple types of exams to
obtain the same information," says Michael
Bleshman, MD, vice chair of the Department of Radiology
at the University of Pennsylvania Health System and chair
of Diagnostic Imaging at Phoenixville Hospital. "Although
CT and MRI are highly effective, some more difficult cases
benefit from the problem solving capabilities of PET. After
undergoing treatment for cancer, patients are often left with
some residual abnormality seen by an anatomic image. Because
PET is a metabolic image it can be particularly effective
in distinguishing if the abnormality is scarring from the
original disease or if it is residual tumor."
PET is effective in many cancers, including malignancies
of the following structures/organs: lung, head and neck, colorectal,
esophagus, lymph nodes, breast, thyroid, ovary, cervix, endometrium,
pancreas, testes and brain. PET is of value in the diagnosis,
staging, monitoring response to treatment and detecting recurrence
following initial and subsequent therapies.
"There is a great deal of ongoing PET research activity
related to cancer at Penn. Our main focus at this time is
studying
primary breast cancer as well as adult and pediatric brain
tumors, neurofibromatosis, and Hodgkin's and non-Hodgkin's
lymphoma," says Dr. Alavi. PET's ability to detect early
disease also has significant implications in diagnosing Alzheimer's
disease, Parkinson's
disease, epilepsy, and other neurological conditions, which
contribute to the management of these patients.
Significant cost and operational factors have previously
kept this diagnostic tool from becoming widely available.
"Patients prefer not to travel significant distances for
diagnostic tests, and now the Penn PET program has allowed
us to bring
this technology into the community," explains Dr. Bleshman.
Integral PET Associates, LLC, Penn's Department of Radiology,
the Abramson Cancer Center of the University of Pennsylvania,
and Penn Cancer Network Hospitals are partnering to offer
this program.
Although PET scans are covered by a wide variety of insurance
companies for many indications, preauthorization is frequently
required.
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