In the diagnosis of breast cancer, anatomic findings on
mammography and ultrasound imaging can sometimes be inconclusive,
particularly in women with dense breast tissue and those who have
natural changes within the breast parenchyma. Functional imaging,
such as Breast-Specific Gamma Imaging (BSGI) with the Dilon 6800
gamma camera (Figure 1), can often overcome these limitations and
provide crucial information that cannot be found with anatomic
imaging.
"In cellular biology, the first thing to change with cancer is
the function, not the gross anatomy," explained Ted Fogarty, MD,
Staff Radiologist at Medcenter One Hospital, Bismarck, ND, and
Chairman of Radiology, University of North Dakota School of
Medicine, and a shareholder in Dilon Technologies. "Mammography
just looks at the anatomy," said Milton J. Guiberteau, MD, FACR,
Chief, Nuclear Radiology in the Department of Medical Imaging, and
Director of the Women's Care Mammography Clinic at CHRISTUS St.
Joseph Hospital, Houston, TX. "BSGI, on the other hand, reveals the
function of the tissue, enabling clinicians to more clearly
determine if the anatomic changes are benign or are suspicious for
malignancy."
The Dilon 6800: Advanced Technology Significantly
Improves Clinical Results
Functional imaging of the breast is not a new concept. It was
first attempted many years ago using a standard gamma camera;
however, the limitations inherent in the older equipment did not
allow for the reliable detection of many cancers, such as
sub-centimeter lesions and DCIS (Ductal Carcinoma In Situ).
Furthermore, the standard gamma cameras were unable to replicate
mammographic views, which made correlation between the functional
and anatomic data difficult.
Unlike other gamma cameras, the Dilon 6800 has been optimized
for breast imaging and is capable of detecting lesions as small as
3 mm. Its sensitivity has been found to be similar to mammography
at approximately 96%, but its specificity is significantly higher
at 92%, and its negative predictive value has been shown to be as
high as 99%. In addition, BSGI with the Dilon 6800 replicates the
patient positioning used in mammography (Figure 2), thereby
providing an easily correlated functional map to the structural
abnormality.
BSGI in Clinical Practice
BSGI is most commonly used for those patients who have equivocal
mammography or ultrasound findings. "Mammography is very good at
detecting cancer in women who have easy-to-read mammogram patterns,
but it's not so good for women who have dense patterns," said
Fogarty, explaining that mammograms of heterogeneously dense and
very dense breasts often are very nonspecific. With BSGI, the
diagnostic quality of the image is not affected by tissue density
or other structural changes, such as scars or implants. "The
sensitivity is the same in both fatty breast and dense breasts,"
said Guiberteau. "We use BSGI on patients with dense breasts who
have findings that are not elucidated by diagnostic mammography,"
he continued, "and in patients who have implants or postsurgical,
post-chemotherapy, or postradiation lesions."
A plus to its utility in initial diagnosis is that BSGI is also
helpful in detecting additional, unsuspected lesions in women with
a known carcinoma. "In patients with a known cancer diagnosis, we
use BSGI to help determine the extent of involvement in that breast
and to gather information about the other breast," said Tricia A.
Kelly, MD, Assistant Professor of Surgery and Associate Director of
the Breast Care Center at George Washington University, Washington,
DC. "In many cancer patients, we have seen additional foci in the
involved breast and we've picked up foci in the opposite
breast."
Such BSGI findings can alter surgical planning and follow-up
regimens. "If we find a second, remote carcinoma, that patient may
no longer be a candidate for breast conservation surgery and might
need a mastectomy," said Kelly.
BSGI may also be used to help clarify lymph node status. "For
example, in a patient with a known cancer diagnosis without any
clinically significant lymph node findings, we may see uptake in
the axilla on the BSGI," explained Kelly. "If we see what looks
like lymph node involvement on BSGI, we may alter what we recommend
as far as a sentinel node biopsy versus axillary dissection."
Integrating BSGI in the Breast Center
The compact, mobile design of the Dilon 6800 allows the system
to be integrated into the breast center, facilitating a smooth
continuum of care and allowing for rapid results for patients'
peace of mind. In fact, in many facilities, patients can proceed
directly from diagnostic mammography to BSGI during the same
visit.
For the patient, the BSGI is nearly identical to the familiar
mammogram, but without the uncomfortable compression. Once the
examination is completed, patients can often get their results
right away. "We always compare our BSGI study with the patient's
mammogram, ultrasound, magnetic resonance imaging studies, history,
and anything else that is available," noted Guiberteau, "but if the
patients are willing to wait a few minutes, we are usually able to
give them their results right away."
Learning Curve
"As for the learning curve, like any exam, the technologist must
be adequately trained to get the proper images, but it can be
readily learned," said Guiberteau. "For physicians reading the
study, I would not say the learning curve is steep, but you have to
be able to distinguish between a focus that looks significant as
opposed to a focus that looks like the background of normal breast
tissue. With the Dilon camera, the interpretation is not
difficult."
"The other learning curve issue is learning to trust the
technology," added Fogarty, "because you are so trained to use
structurally suspicious findings to determine how to proceed. Early
on, we did some biopsies on things that had shown up as shadowing
areas on ultrasound or consistent masses under compression, but the
findings on BSGI were negative, so we began to trust the technique
more."
Case Report
An 82-year-old woman with moderate bilateral stable dense breast
parenchyma presented with a new nodular density that was noted on
mammography (Figure 3). The findings were classified as BIRADS 4,
with no cysts or solid masses noted on the ultrasound
examination.
The patient underwent BSGI, which showed two foci of significant
uptake (Figure 4). One was consistent with the nodular density
noted in the mammogram and the other was within the area of stable
dense breast tissue. The histopathology findings for this patient
indicated infiltrating ductal carcinoma in both sites. In this
case, BSGI detected a second site of carcinoma that had not
previously been located with other modalities, thereby changing the
course of treatment for this patient.
Conclusion
"This is one of those cases in medicine in which not only is it
a great piece of technology, it's actually a money-saving use of
resources," concluded Fogarty. "When we find a 1-cm cancer with
BSGI on a woman who has a total white-out on a mammogram and we are
able to catch it as stage 1 disease, we end up saving the
healthcare system hundreds of thousands of dollars and we save that
woman's life."
Contact Information
Dilon Technologies LLC
12050 Jefferson Ave, Newport News, VA 23606
877.GO DILON info@dilon.com
www.dilon.com