Breast cancer is the second leading cause of cancer death in women, exceeded only by lung cancer. The chance that breast cancer will be responsible for a woman's death is about 1 in 35 (about 3%). In 2008, about 40,480 women will die from breast cancer and 250,230 women will be diagnosed with breast cancer in the United States, as estimated by the American Cancer Society. However, if detected and treated early, more than 95% of breast cancer patients will survive. Current screening methods for breast cancer rely heavily on X-ray mammography, which while effective and relatively low cost, produces many false positives. These false positives cause substantial mental anguish and in many cases, costly and painful biopsies. It is estimated that 960,000 negative biopsies are performed annually in the U.S. alone, at a cost of 2.5 billion dollars (details). These negative biopsies constitute a full 80% of all biopsies performed (details), uncovering only benign masses and calcifications. Thus there is a great need for the development of a complementary, diagnostic method capable of reducing the number of false positives in X-ray mammography readings. Most importantly, this diagnostic method must be accurate and low cost due to the large numbers involved.

Positron Emission Tomography (PET) has great potential as a complement to X-ray mammography for reduction of unnecessary biopsies. It has been shown to be a very effective imaging tool for the detection and characterization of tumors of various cancers. Cancerous cells have higher glucose metabolism than normal cells, and thus malignant tumors show up as “hot spots” in PET scans utilizing the imaging tracer ¹⁸F-FDG, a positron emitting radioisotopically labeled glucose analog.

The current clinical setting for PET is dominated by whole body imaging systems, which are large and cumbersome in size and expensive in both upfront investment and maintenance costs. While they are capable of scanning the breast region, these systems are much less adequate when compared with a dedicated Positron Emission Mammography (PEM) scanner for several reasons. The most important advantage that a dedicated PEM scanner provides is increased sensitivity for radiation detection with vastly reduced detector size and cost. Current PEM imaging devices are in early developmental stages and all utilize crystal-based radiation detectors. The focal problem with these detectors in this application is that deep crystals on the order of 3 cm are required to reach high sensitivities. In the PEM application, in contrast to whole body cameras, the lack of knowledge of depth of interaction (DOI) produces a great reduction in resolution because of the larger solid angle acceptance required.

Proportional Technologies Inc. has employed its unique lead-walled straw detector in the development of a positron emission tomography (PET) camera, dedicated to breast functional imaging

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Figure 1: Proposed detector system composed of two arrays of lead walled straw detectors. (left) Side view of camera showing detectors, track and rotating gantry. (right) Top view of the camera showing how the two detectors can be adjusted to accommodate variable organ dimensions and to facilitate imaging during compression if desired. The entire camera can be retracted from beneath the bed to provide access for biopsy procedures.

The new breast PET camera has clear advantages over conventional crystal-based cameras, such as lower cost, no depth-of-interaction errors, no photomultiplier tubes, accurate 3D position encoding, and uniform sensitivity and resolution over the entire FOV

Figure 2: A prototype breast PET camera, consisted of 6 detector modules.

Funding

This technology has been funded by the NIH under the project name "Straw Detector Positron Energy Mammography System" - CA117222