In cancer treatment physicians have longed for a way to locate the tiniest of tumors, information that can be the deciding factor in the course of effective treatment. This is one of many medical applications for a technology that has been making its way to the forefront of diagnostic imaging in the past several years. It’s called positron emission tomography, or PET, and medical researchers and clinicians are marveling at the information it offers about the human body.
PET traces its roots to St. Louis. A team of researchers at Washington University’s Mallinckrodt Institute of Radiology developed the first PET instrument for human studies. The Institute continues to make significant contributions to the ongoing development of PET.
Based on scientific advancements in the 1930s, PET equipment was first developed in the 1970s. Since its introduction, PET has been used for a wide variety of research. PET data have particularly enhanced understanding of the brain, heart and lungs. Using PET, researchers have explored the basic physiological changes associated with conditions such as Alzheimer’s disease, epilepsy, stroke, schizophrenia, and Parkinson’s disease. PET studies also include aging, depression, multiple sclerosis, substance abuse, lung function and tumors.
Michael J. Welch, Ph.D., professor of radiology and research administrator at the Mallinckrodt Institute at Washington University, differentiates PET from other imaging, “PET looks at physiology rather than anatomy. In other words, imaging techniques such as X-ray, ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI), provide a map of the body’s roadways, its anatomy; PET shows the traffic along those paths, its biochemistry.”
James Eikmann, an assistant administrator with responsibility for radiology at Saint Louis University Hospital (SLUH) adds, “PET is ideal for locating and identifying tumors. It aids the physician in selecting appropriate treatment and determining effectiveness of treatment.”
How PET Works
In PET studies, a cyclotron is used to produce a “radiopharmaceutical,” which is a short-lived radioactive compound of a substance normally found in the body. For example, glucose can be tagged with fluorine-18 to trace its metabolism where tumors are suspected. In addition to their use in cancer detection, this technique also allows researchers to study brain and heart functions. As the nuclides decay, they emit positively charged electrons or positrons. After administering the radiopharmaceutical or tracer to the patient, the PET device’s circular array of scanners detect the release of the decay event, sending information to a computer that reconstructs the distribution of the radio-nuclides in a patient and then displays the information. The more active a part of the organ being studied, the greater the concentration of positron emissions.
According to Dr. Welch, the major benefits to patients have developed recently, over the past seven years, even though PET was introduced nearly three decades ago. PET is particularly valuable in determining a course of treatment for certain cancer patients.
Val Lowe, M.D. and Medical Director for SLUH’s Radiology Department explains, “An oncologist, or cancer specialist, may have detected the existence of one tumor in a lung cancer patient. If there is only one tumor, a prudent course of treatment would be surgical removal of the tumor. However, when multiple tumors are present, experts recognize surgery is inadequate and recommend another treatment such as radiation or chemotherapy.”
In this instance PET is valuable in two ways. First, X-ray or CT scan normally cannot detect this type of tumor. Second, in measuring the metabolism of the glucose, PET can detect the existence of tumors as small as five millimeters. Detecting an early spread of tumors can spare a lung cancer patient from surgery and move on to a treatment that will more successfully prolong life.
“PET increases probability of a correct diagnosis and treatment decision to 90 percent versus 67 percent with X-ray or CT,” Dr. Lowe states.
PET is also very safe and non-invasive for the patient. No incisions or anesthesia are required. And the level of radiation exposure is mild, similar to a chest X-ray.
Both Dr. Lowe and Dr. Welch say that using different tracers, researchers, have made new strides understanding other conditions such as how stroke or head injury affects the physiology of the brain. Also, physicians may use PET to determine the effectiveness of certain treatments for cancer, stroke, head injury and epilepsy.
PET’s Future
Last year, Medicare approved reimbursement for PET use in diagnosis and treatment determination for cancer. Private insurance payers already had been reimbursing for PET scans for nearly all diagnoses.
Though PET equipment is expected to become widely used in diagnostic facilities, Dr. Welch says currently there are only 150 PET scanning devices in use worldwide. With two teaching hospitals and the accompanying research facilities, there are six PET scanners in St. Louis. Four of the devices are within the Washington University Medical Center. Three, for research use, are part of the Mallinckrodt Institute of Radiology and one of those is in the Barnes-Jewish Hospital Neuro-ICU for use in a head trauma study. A fourth unit is also at Barnes-Jewish for strictly clinical use, primarily for tumor detection. Washington University’s two cyclotrons, needed to produce the radiopharmaceuticals, supply for both research and clinical uses.
Saint Louis University Hospital currently operates two PET scanners and one cyclotron. In addition to detecting lung cancer tumors, SLUH’s Nuclear Medicine Department is having success using PET in detecting lymphoma and melanoma, as well as cancers of the brain, head and neck, breast, colon and liver. Eikmann and Dr. Lowe say the PET scan is also in use for SLU Medical School’s participation in research on other cancers.
In addition to St. Louis, PET scanners are in three other midwestern cities: Chicago and Peoria, Ill., and Madison, Wis. Obviously, many patients from the region are referred to either Barnes-Jewish or SLUH for PET scans when needed.
Though the Food and Drug Administration (FDA) approved the use of PET scans 15 years ago, broad approval for clinical use will be released this year. The Health Care Finance Authority (HCFA) last year recommended additional rulings from the FDA regarding the regulation of the radiopharmaceuticals, reports Duffy Cutler, Ph.D., medical physicist and assistant professor of radiology at Mallinckrodt Institute. He adds, an agreement approved by Congress and the Department of Health and Human Services should “un-complicate” this process, but many in the medical and financial communities are watching implementation of this agreement before making additional investments in PET technology.
Another factor with a radiopharmaceutical used for PET scanning is that with a short, two-hour half-life, the radiopharmaceutical must be produced nearby where it will be used. Also, the techniques and equipment, such as the cyclotron, necessary to create radiopharmaceuticals are under strict government guidelines. Only hospitals and diagnostic facilities able or willing to meet those requirements will be installing PET.
The future of PET is important to St. Louis and patients worldwide. Dr. Welch says St. Louis benefits from the attention of $9 million each year in research grants to Washington University School of Medicine for PET studies, which attracts some of the world’s best researchers. Also, he says Mallinckrodt, Inc., a St. Louis-based company that is one of the primary radiopharmaceutical producers in the country, is likely to benefit from increased PET use – which will, in turn, affect St. Louis’ economy.
Dr. Welch travels the nation and world to inform the medical community about the advantages of PET. In June three international symposiums on radiopharmacology, hosted by Washington University School of Medicine, brought more than 500 physicians and scientists to St. Louis.
With more than 2,000 tracers in use for PET medical research and many promising developments in areas such as neurology, Dr. Lowe predicts several additional clinical applications will be in use in the next decade.
