July 27, 2009
Postcards From Toronto
Radiology Today
Vol. 10 No. 14 P. 18
Editor’s note: This article is based on material provided by the SNM media relations department and presented in press conferences at the organization’s 56th annual meeting last month in Toronto.
New Approach for Treating Recurrent Prostate Cancer
Researchers have indicated that an alpha-particle–emitting radiopeptide is effective for treating prostate cancer in mice. Radioactive material bound to a synthetic peptide could eventually result in a significant breakthrough in prostate cancer treatment, especially for patients whose cancer recurs after the prostate is removed.
“Our study shows that this novel form of treatment has the potential to target and destroy cancer cells with minimal damage to surrounding healthy tissue,” said Damian Wild, MD, of Switzerland’s University Hospital Basel and the study’s lead author. “Eventually, this therapy could give hope to some of the hardest-to-treat prostate cancer patients and also could be applied to other types of cancer.”
Because tumor cells readily bind with certain peptides, researchers have been able to develop highly specific radiopeptides that bind with tumor cells and treat them using specific therapeutic radioactive substances attached to the radiopeptide. Prostate cancer cells—and many other types of cancer cells—have an overabundance of gastrin-releasing peptide receptors, making the cancer a strong candidate for treatment with radiopeptides.
The study compared two different types of radiopeptides. One group of mice was injected with 213 Bi-DOTA-PESIN, which emits alpha particles that are effective for killing cancer cells. The other group was injected with beta-emitting 177 Lu-DOTA-PESIN, which is also effective for tumor cell killing but can cause damage to nearby healthy cells. Alpha particles are able to kill cancer cells without damaging surrounding healthy tissue. A third group of mice received no treatment.
However, at the maximum tolerated dose, the alpha-emitting 213 Bi-DOTA PESIN was significantly more effective, tripling the survival rate of the mice that received the therapy. The results indicate that the alpha-emitting radiopeptide could provide a new approach for treating prostate cancer and eventually other types of cancer.
More than 186,000 men in the United States are newly diagnosed with prostate cancer each year. More than 30,000 men each year who have had their prostates removed experience cancer recurrence. In most of these cases, the disease cannot be localized and treated adequately with conventional treatments; therefore, a systemic treatment that efficiently kills small tumors is needed.
Improving Cardiac PET Images
Combining high-definition PET and a “motion-frozen” image-processing technique that compensates for the motion of the beating heart provides enhanced cardiac images, according to researchers. A new study of the combined technologies shows that the method provides exceptional PET image quality and can significantly change the diagnosis of patients with heart disease.
The motion-frozen technique is designed to remove unwanted blur and thus improve the diagnostic value of imaging. The researchers found that the resulting images include physiological details that were previously invisible to physicians using PET imaging.
“Our study shows that combining these technologies revealed defects that otherwise would not have been imaged,” said Ludovic Le Meunier, senior scientist at Siemens Healthcare Molecular Imaging in Hoffman Estates, Ill., and Cedars-Sinai Medical Center in Los Angeles. “While our study was limited to a specific imaging test, the findings could indicate a whole new level of quality in cardiac imaging and could significantly advance the ways that physicians diagnose and treat heart disease.”
PET myocardial viability assessments are commonly prescribed for heart failure patients to assess the heart’s muscular wall and help physicians decide on treatment. However, cardiac PET image quality can be limited by the physiological motion of the heart, which can distort images, and by certain shortcomings in PET scanners.
For the study, images of the heart were obtained by combining a high-definition Siemens PET scanner with Cedars-Sinai’s motion-frozen technology. The high-definition PET scanner uses “spatially variant detector spatial response” when the image is reconstructed, correcting for distortion and noise that can make images hard to interpret. The motion-frozen technology was originally developed by Piotr Slomka, PhD, a research scientist at Cedars-Sinai Medical Center.
In the study, the combined technologies were used to obtain images of 10 patients who were referred for PET myocardial viability assessments at Cedars-Sinai. For these patients, the diagnostic results were modified after imaging with the new technologies—sometimes drastically.
Researchers are investigating expanding this technique to correct for the distortions that arise from respiratory motion during imaging. Preliminary results of a separate study on that application of the motion-frozen technique were presented during the SNM annual meeting.
PET Finds Infection Cause in Knee Replacements
PET scans accurately detect infections in prosthetic knee joints more than 90% of the time, according to new research.
“Infections following joint replacement surgery are very serious, very common, and very difficult to distinguish from other problems such as loosening of the prosthetic,” said Abass Alavi, MD, a professor of radiology at the University of Pennsylvania in Philadelphia and the study’s principal investigator. “Our study shows that no other diagnostic tool comes close to PET in accurately diagnosing infection with minimal discomfort for patients. What’s more, the broader implication is that PET could eventually be used to successfully detect infections and inflammation for other conditions.”
It is estimated that more than 1 million joint replacements are performed in the United States each year. Infections following implant procedures are difficult to fight because the immune system is unable to destroy bacteria that live on the implanted material. Even after treatment with strong antibiotics, the infections can persist. As a result, it is often necessary to remove prosthetic joints if they become infected.
Accurately determining whether pain in a prosthetic joint is an infection can be difficult. Physicians often have to operate without accurate information on whether an infection is occurring. The most common technique used to determine infection is the white blood cell count; however, the test is only about 50% accurate, is at least two times more costly than PET, and takes longer to provide results.
In the study, 80 patients who were experiencing painful knee symptoms underwent FDG-PET imaging after clinical evaluation and laboratory data were inconclusive for infection. Of these patients, 50 were available for full follow-up. Clinical outcomes were determined via surgical, microbiological, and other clinical indicators. PET images were interpreted to indicate infection if there was increased FDG uptake at the bone-prosthesis site.
Overall, FDG-PET imaging was 92% accurate, correctly diagnosing eight of the nine cases of infection and identifying the absence of infection in 38 of 41 cases.
SPECT Provides High-Quality Images of Small Tumors
Combining high-resolution and high-sensitivity collimation provides better quality SPECT, according to new research.
Collimators are used in SPECT because it is not yet possible to focus radiation with such short wavelengths into an image with the use of lenses. Using the two types of collimation in tandem is especially effective for better imaging of small tumors, according to the study.
“SPECT is an important tool in molecular imaging because of its ability to provide accurate images of what is going on in the body without the need for invasive procedures such as surgery,” said Roel Van Holen, PhD, a researcher in the department of electronics and information systems at Ghent University in Belgium and the study’s lead author. “However, researchers have had to make trade-offs in SPECT image quality, especially in imaging very small tumors. Our research is exciting because it shows that combining high-resolution and high-energy collimators can improve SPECT’s ability to image small tumors.”
Researchers have established that SPECT image quality generally improves when using collimators with higher sensitivity than traditional low-energy, high-resolution collimators. However, this is not the case when small tumors are being imaged. In these cases, low-energy, high-resolution collimators actually provide better images.
The new study combined a high-resolution collimator with a high-sensitivity collimator. A dual-head SPECT camera with three different collimator settings was simulated using the GATE Monte Carlo simulator. The results indicate that SPECT image quality was better with the mixed collimation than it was by using only high-resolution or only high-sensitivity collimation.
PET May Improve Dementia Diagnosis Accuracy
PET scans may improve the accuracy of dementia diagnoses early in disease onset for approximately 25% of patients, according to research results.
“Routine clinical assessments do not accurately identify the root causes of dementia in the early stages,” said Kirk A. Frey, MD, PhD, a physician with the University of Michigan Hospitals’ division of nuclear medicine and the study’s lead author. “Our preliminary results clearly indicate that molecular imaging technologies, such as PET scans, can help diagnose a patient’s specific type of dementia. This is critical for providing the best possible care. Additionally, PET’s ability to pinpoint neurological underpinnings of different forms of dementia could lead to new, more targeted drugs and therapies.”
The new study identified 66 patients with mild dementia or mild cognitive impairment who were evaluated through standard neurological testing and anatomic brain imaging. Three clinical experts reviewed the results of these data to make diagnoses of either Alzheimer’s disease, frontotemporal dementia, or dementia with Lewy bodies. Patients then underwent PET scans for amyloid deposits and dopamine nerve integrity. Patients’ initial diagnoses changed more than 25% of the time after PET imaging. PET scans provided images of important signals for disease that other examinations missed, such as deposits of amyloid plaque, which are a common indicator of Alzheimer’s disease, and damage to dopamine nerves in Lewy body dementia.
The study will track patients for two years to confirm the accuracy of their diagnoses.
