Positron imaging joins x-ray mammography alternatives

October 1, 2007

Small-field-of-view positron imaging, optimized for breast cancer detection, is jockeying for position among several adjuncts to x-ray mammography. A proponent of the technology, Dr. Kathy Schilling, believes it has an edge over MRI.

Small-field-of-view positron imaging, optimized for breast cancer detection, is jockeying for position among several adjuncts to x-ray mammography. A proponent of the technology, Dr. Kathy Schilling, believes it has an edge over MRI.

Preliminary work done by Schilling and colleagues at the Center for Breast Care in Florida's 400-bed Boca Raton Community Hospital has made her optimistic that positron emission mammography (PEM) will become the definitive tool not only in diagnosis of breast cancer but in screening and preoperative planning as well.

Results from a pilot study of women with biopsy-proven breast cancer presented at the Society of Nuclear Medicine meeting in June indicate that the technology is more helpful than MRI in preoperative planning. The study documented that PEM, with both sensitivity and specificity greater than 90%, was as sensitive as MRI in detecting invasive and noninvasive breast cancer and could identify atypical pathologies better than breast MRI.

"Everything is moving to molecular imaging," said Schilling, director of breast imaging and intervention at Boca Raton. "I think this will be breast cancer's molecular imaging tool."

Boca Raton Community Hospital, which does some 55,000 breast exams annually, routinely applies PEM as part of a research protocol aimed at determining the clinical value of the fledgling tool. PEM images are interpreted by a staff of six radiologists.

With an intrinsic resolution between 1.5 mm and 2 mm, PEM has obvious applications as an adjunct in breast cancer diagnosis and possibly screening. The technology characterizes small lesions metabolically, potentially spotting malignancies at an earlier stage than any other technology, according to Schilling.

Unlike MRI, which requires substantial training to interpret the enhancement patterns created using injected contrast media, PEM allows expert interpretation after experience with five to 10 cases, said Schilling, who teaches breast MRI to physicians.

"So many things light up in patients having MRIs, especially patients who are perimenopausal or on hormones," she said, noting that these problems do not affect PEM. "There are a lot fewer false positives on PEM compared with breast MRI, and yet it is just as sensitive."

Physicians specializing in women's health are easily frustrated by breast MRI, Schilling said. Not only is it difficult to interpret images, but scheduling patients on a busy scanner can be a problem.

"So this will be an alternative for these somewhat frustrated physicians," she said.

The PEM cases at Boca Raton are captured using a small-field-of-view PET camera from Naviscan PET Systems. The FDA-cleared device, called the PEM Flex Solo II, needs no special shielding or wiring and takes about the same space as x-ray mammography equipment. PEM views of the breast obtained with the patient seated are comparable to those obtained using x-ray mammography, whereas MR images captured when the patient is supine are difficult to match with mammograms.

Access to FDG, the positron-emitting workhorse of the PET community, is a must, but if the radioisotope is there, so is the money. Reimbursement for FDG exams of the breast is widely available, according to Schilling.

One big challenge remains, however. The PEM Solo Flex II does not image the axilla, which may harbor metastatic breast cancer. Schilling and colleagues get around the problem by doing a whole-body PET exam to look for these lesions.

"This means we are doing two exams and charging for only one," she said. "But if you want all the information, that's what you do."

Currently, physicians typically use just two modalities, mammography and ultrasound, to screen for breast cancer, referring patients with suspicious lesions for biopsy. Recent studies have shown the value of using MR as an adjunct diagnostic aid or even as a screening tool. PEM may be even better, at least under specific circumstances, according to Schilling. She and colleagues are conducting research that may help determine whether this optimism is warranted.

They are focusing particularly on patients scheduled for lumpectomy. PEM has the potential to find more and smaller malignancies compared with breast MRI. Schilling wants to document outcomes following evaluation with each modality, while comparing them with surgical management of the patient, currently the gold standard of breast cancer care, she said.

Their research will be bolstered by results from four other medical centers that are assessing the use of PEM and breast MRI in presurgical staging of breast cancer. The other centers are Anne Arundel Medical Center in Anne Arundel, MD; Scripps Cancer Center in California; American Radiology Services/Johns Hopkins in Breen Spring, MD; and the University of North Carolina in Chapel Hill. Schilling said she is confident that, when the results are tallied, PEM will be the clear choice in the diagnosis and screening of breast cancer.