|
|||||||||||||||
|
Home
|
Molecular Imaging
Techniques Add Versatility to Breast Cancer Diagnosis Clinicians are taking advantage of new vantage points and perceptions about cancer development by adapting nuclear medicine techniques for use as diagnostic and treatment planning tools. Mammography is still the primary breast cancer screening tool, and newer techniques such as breast MRI and breast sonography have contributed considerably to our knowledge about the disease. However, in some cases, all these modalities raise questions that doctors are ill-equipped to answer, which can lead to unnecessary biopsies or missed cancers. Some answers can be found outside the realm of anatomic imaging in nuclear medicine. Advances in molecular breast imaging procedures—specifically breast-specific gamma imaging (BSGI) and positron emission mammography (PEM)—are providing clinicians with new information by visually portraying the metabolic activity of breast lesions through radiotracer uptake. This functional data helps them better differentiate between benign and malignant tumors, find cancer at earlier stages, and chart treatment courses. BSGI and PEM are not screening tools and by no means meant to replace mammography, nor are they supplanting adjunctive MRI and ultrasound tools. Rather, they’re being used as an alternative and even as an adjunct to an adjunct. Gamma Camera Perspective BSGI evolved from scintimammography. Early on, this nuclear medicine imaging technique demonstrated potential in diagnosing breast cancer; however, standard gamma cameras limited its image correlation with mammograms, as well as its ability to identify lesions less than 1 centimeter. But subsequent development of anatomic-specific gamma detectors opened the door to higher resolution functional breast imaging. “Researchers came up with a very good dedicated breast detector that essentially employs the same imaging platform as mammography,” relates Sheldon Feldman, MD, chief of the Appel-Venet Comprehensive Breast Service at the Beth Israel Medical Center in New York City. “With BSGI, standard mammographic views are acquired from the top and side, which generates images that look very much like a mammogram, but these are enhanced with a radiotracer. This enables us to see areas of increased radioactivity, which indicates increased metabolic activity, a characteristic of cancer.” In early 2006, acting on Feldman’s recommendation, the Beth Israel Medical Center became the first hospital in New York City to use BSGI to help identify cancerous breast tissue undetected by mammography. Specifically, Beth Israel equipped itself with the Dilon 6800 camera developed by Dilon Technologies LLC of Newport News, Va. “As I talked about it with my radiology colleagues, it became clear to me that this was a significant advance in breast imaging,” says Feldman. Optimal Detection Like Beth Israel, George Washington University uses the Dilon BSGI 6800 camera. “We use it in virtually all newly diagnosed breast cancers and for the screening of high-risk patients,” Brem says. “It helps us find cancers that can’t be seen with mammography and ultrasound. It’s an integral component of our practice.” As BSGI images are obtained at the molecular level, exams aren’t compromised by tissue density, helping clinicians detect early stage cancers. In addition, because of its high accuracy rate, BSGI helps reduce the number of unnecessary biopsies, and it provides a powerful presurgical planning tool, which helps preserve healthy breast tissue. “Our surgeons rely on it to help with surgical planning because it not only shows what the cancer looks like, but it shows how much of the breast it physiologically encompasses,” says Brem. Besides surgical planning, BSGI helps detect breast cancer in patients with problematic mammograms who need further evaluation, such as women with prior breast surgery, dense breast tissue, breast implants, multiple suspicious lesions, or palpable lesions not detected by mammography or ultrasound. Feldman adds that BSGI is especially important for diagnosing high-risk patients. “Risk is based on family history, atypia, and a previous diagnosis of breast cancer,” he says. Patients at the highest risk, he adds, are those with the BRCA1 gene mutation. “Their surveillance needs to be careful and diligent. As such, we provide for them a yearly mammogram, a target sonogram of areas of interest, a yearly breast MRI, and BSGI. In the past, we did two breast MRIs. Now, we do one MRI and a BSGI,” he says. Measured Against MRI Also, interpretation is more rapidly accomplished with BSGI, and patients can often receive same-day results. “We’re only looking at four to eight images as compared to 800 images with breast MRI,” Brem points out. BSGI is also less expensive and more patient friendly. It requires only a minimal amount of breast compression and, as it’s an open exam, patients don’t suffer claustrophobia. “From the patient standpoint, the only drawback might be that the procedure requires an intravenous injection,” says Feldman. During the procedure, a patient receives a small amount of radiotracer (Technetium-99m), which is then absorbed by the body’s cells. The tracer emits gamma rays detected by the gamma camera and converted into a digital image of the breast. Cancer cells have high metabolic activity and absorb a greater amount of the radiotracer. Imaging begins almost immediately, and during the acquisition process, the patient rests comfortably in an upright position. Each view may take only six to 10 minutes to acquire. BSGI is also user-friendly. “It’s easy to obtain multiple views that correlate with the mammograms,” says Feldman, “and the learning curve, for both radiologists and technologists, isn’t that steep.” Moreover, BSGI equipment costs significantly less than many other modalities, and it’s rather easy to implement. “This isn’t a gigantic piece of equipment, so a dedicated room isn’t required. In fact, the camera is small and portable, so it can be moved from room to room, site to site,” says Feldman. As such, the technology can be reasonably adapted by most facilities that have nuclear imaging capability. The hospital setting is a particularly suitable environment, Feldman points out: “After all, this is a nuclear imaging procedure, and all large hospitals have nuclear imaging departments.” The PEM Option Currently, PEM is primarily the province of Naviscan PET Systems, Inc. The San Diego-based company has developed the PEM Flex PET Scanner, an organ-specific PET device optimized to image breast cancer, as well as the second generation PEM Flex Solo II, which features photonics improvements that yield higher count-rate sensitivity while maintaining resolution capabilities of 1.5 to 2 millimeters (the highest offered by any biochemical breast imaging modality, according to the company). This resolution helps improve treatment planning and, combined with functional imaging capability, enables the system to improve lesion characterization. Also, the resolution enables the system to image ductal carcinoma in situ, something that’s quite difficult to accomplish—if not impossible—with mammography, breast MRI, and other modalities. “PEM [resolution] is right in the range of ductal size, which is where cancer typically originates,” says Kathy Schilling, MD, medical director of breast imaging and intervention at the Center for Breast Care at the Boca Raton Community Hospital in Florida, where Naviscan PEM technology was implemented nearly one year ago as an alternative to, but not necessarily a replacement for, breast MRI. “Currently, we’re using the technology as a purely investigational imaging procedure, predominantly with patients recently diagnosed with breast cancer, looking for additional unsuspected disease and comparing the findings with that of breast MRI.” PEM Procedure The patient-friendly procedure can be accomplished in less than one hour. During the imaging, PEM detectors are positioned close to the breast, making acquisition more efficient. While the breasts are immobilized, only slight compression is required. Further, like BSGI, PEM is a seated, open exam. “There are no claustrophobia issues,” she adds. Schilling says PEM’s advantages include the following: • It delivers high resolution and improved specificity and sensitivity. • It produces fewer false positives. “For me, that’s the most important thing,” Schilling says. • It allows efficient follow-up by whole-body PET. “We can follow PEM with whole-body PET imaging. In essence, you get two exams with one injection. In certain patients, this can reveal metastatic disease,” Schilling says. • It supports efficient image interpretation. “One of the biggest advantages is that you’re only looking at about 48 images,” Schilling says, “as opposed to thousands with MRI.” Again like BSGI, PEM is not difficult to implement, presuming your facility has the capacity to handle radiopharmaceuticals. “You don’t need the kind of dedicated room that you need with MRI, so it’s a lot simpler to integrate into a practice,” says Schilling. It’s also easier to learn how to interpret PEM images than breast MRI images. “There’s been a lot of frustration with breast MRI, not only because of the variability in acquisition and interpretation of exams, but it’s also difficult to institute a breast MRI program,” says Schilling. Comparative Study Schilling says the results found that PEM resulted in fewer false positives and was as sensitive in identifying breast cancer as breast MRI but had better specificity. Also, PEM helped identify areas of atypia better than breast MRI. “In the future, this may assist us in evaluating patients at the highest risk—the BRCA1 patients—for developing breast cancer. In addition, by identifying areas of atypia, we may be able to offer patients prophylactic medical or surgical therapies, if they know they are at increasing risk. So PEM could become an even more important tool,” says Schilling. In assessing PEM’s future impact, Schilling says, “As breast imaging evolves and becomes more sophisticated, I think we’ll be seeing more regional breast centers, and PEM will find a place in the centers that want as many tools as are available to maximize the number of cancers found and to find the cancers at the earliest stages. If such a center has a high-risk clinic, then PEM will be an integral part.” — Dan Harvey is a freelance writer based in Wilmington, Del. He is a frequent contributor to Radiology Today. Is your facility pursuing breast PET, BSGI, or MRI?
Share the reason behind the selection here.
|
|
3801 Schuylkill Rd • Spring City, PA 19475 Publishers of Radiology Today All rights reserved. |