“I think PET/CT is becoming de facto practice in many oncology scenarios,” says Kevin Berger, MD, director of PET imaging at Michigan State University, department of radiology in Ann Arbor. That’s the case for lung cancer and becoming true for a broader range of cancers, he says. Berger uses GE Healthcare’s Discovery STE 16.
PET/CT has proven to be effective in measuring treatment response in numerous cancers, including colorectal, lymphoma, breast and esophageal. Since cancers have a higher energy requirement and therefore accumulate tracers such as fluorodeoxyglucose (FDG) at a greater rate, clinicians can obtain valuable information about the activity of the tumor. “We can use the PET camera to detect distribution of this tracer and see where their cancer is and see what the change in that effect is.” The ability to see how active the tumor is makes it easier to pinpoint and decide how to treat.
Berger says he recently spoke with a thoracic surgeon about the impact PET/CT has had on his practice. The surgeon does an initial PET staging study on every lung cancer patient and “has been amazed how many times that changed his management from prior to using PET.” With a rate of change hovering around 30 percent, “it can make a huge difference.”
The ability to find unsuspected metastatic disease, for example, indicates that the patient is not a good surgical candidate. That prevents patients from undergoing surgery that probably wouldn’t have any benefit. However, with PET/CT, unexpected disease is less and less common, Berger says. Because of better initial staging, patients are getting more appropriate and effective therapy the first time around. In some cases where the patient was not resectable initially, restaging after chemoradiation that shows good response can indicate that the patient has become a good surgical candidate. Appropriate therapy at all points of treatment certainly benefits the patient’s outcome.
PET/CT is “absolutely changing patient outcomes,” says Shyam B. Paryani, MD, MS, MHA, director of Florida Radiation Oncology Group (FROG) in Jacksonville and vice president, Integrated Community Oncology Network. The 60-physician oncology group uses Biograph duo and Biograph 6 PET/CT scanners from Siemens Medical Solutions for treatment planning, which started in 2000.
The hybrid modality helps oncologists target the radiation more exactly and effectively and measure response to treatment. “For about 50 to 60 percent of patients, if you do the PET versus just CT planning alone, that alters the treatment,” says Paryani. “If you don’t do PET, you’ll have inaccurate targeting of radiation.” That rate of change is “tremendous,” he says. “That’s pretty dramatic for one test to affect that many patients.”
Once treatment commences, PET/CT is “very useful in virtually all patients” for detecting therapy response. The major differentiator, Paryani says, is that CT cannot tell whether the cancer is still alive. “By measuring glucose uptake, we actually get a metabolic view and know whether the cancer is still alive and functioning.”
True V technology from Siemens lets FROG scan patients in about half the time—less than 10 minutes versus 15 to 20 minutes—with greater accuracy and improved patient comfort. Paryani says they can detect 4 millimeter nodules while previous technology detected nodules about twice that size. “This is a great leap in technology,” he says.
In the future, results from the National Oncology PET Registry will help determine other types of cancer for which PET/CT is helpful. Paryani expects the results within the next year or two, but preliminary results indicate that the modality is “effective in more cancers than we think.”
Although PET/CT is an expensive technology, “we think it’s the correct technology,” Paryani says. “We can’t manage care without it.” In fact, he says patients who aren’t scanned with PET/CT are “compromising their care.”
|Can phantoms bring real benefits?|
|Paul Kinahan, PhD, professor of radiology and director, PET/CT Physics at the University of Washington in Seattle, is particularly interested in PET/CT’s ability to monitor cancer progression or regression. Although detection is its bread and butter for clinical imaging, the modality is being used more and more to assess response to therapy.|
Research to advance PET/CT is well underway. Manufacturers are working on methods to compensate for respiratory motion, Kinehan says. “Since PET scans take several minutes at best and up to half an hour, there’s a lot of breathing which blurs the image.”
Another area under development is time-of-flight imaging. This method of using faster detectors in the PET scanners measures the speed of light of the photons—the radiation coming from the patient.
An effort Kinehan is personally involved with is comparing scanners across the United States. He and others have been sending the same phantom object—roughly a 10-pound equivalent to the human abdomen with a permanent radioactive source inside—to various PET centers where it has been imaged on 10 different systems from a variety of vendors. “Ideally, every scanner would give the same number, but they don’t,” he reports. The actual numbers are very important when measuring response to therapy. Initial results are showing approximately 8 percent variability. Kinehan and his group will present the initial results at the Society of Nuclear Medicine annual meeting in June.
The results are particularly helpful for clinicians setting up clinical trials. “This will tell them the errors they can expect,” he says. “We want to know whether the difference is due to real biological change or just random noise and other factors. Knowing the variability allows you to determine the statistical chance of real change.” Another arm of the effort is looking to see whether PET centers can use a calibration phantom model to improve accuracy. “It’s a very exciting time to be involved in it,” Kinehan says.