New Technology to Enhance PET Imaging of Breast Cancer

Institution: Stanford University
Investigator(s): Craig Levin, Ph.D. -
Award Cycle: 2006 (Cycle 12) Grant #: 12IB-0092 Award: $154,879
Award Type: IDEA
Research Priorities
Detection, Prognosis and Treatment>Imaging, Biomarkers, and Molecular Pathology: improving detection and diagnosis

Initial Award Abstract (2006)
Positron Emission Tomography (PET) has not yet had significant impact upon breast cancer management because it is currently impractical for routine breast imaging. Currently employed PET systems cannot see breast cancer lesions smaller than about Ĺ inch. Furthermore, standard systems are quite large, very expensive, and require long scan times. Thus, the current role for PET in breast cancer management is limited to identifying advanced or recurring disease in a location removed from the breast clinic. In PET a small amount of a radioactive chemical is introduced into the body. The radiochemical is designed to accumulate in increased amounts in cancer cells due to their increased biochemical activity (rather than structural properties). A PET system images a form of energy called photons emitted from the radiochemical. We will directly address the limitations of existing PET technology by developing an advanced, compact, cost effective system dedicated to breast imaging in the breast clinic. In this project, we propose to explore a novel photon sensing technology appropriate for this high-performance PET camera. The new photon sensor proposed is made from a crystal of the elements cadmium, zinc, and telluride and configured in a special way to form a novel breast-dedicated PET system with superior lesion visualization, shorter scan time, and a factor of 10 lower cost.

The proposed research will experimentally demonstrate the high performance of the photon sensors, verify they lead to improved cancer visualization using computer simulations, and result in a blue-print design of the proposed full breast-dedicated PET system to be built in the next phase. Our aims for this project include:
1. Build and test four photon sensors.
2. Procure electronics that will capture the sensor electrical signals onto a computer.
3. Arrange two pairs of adjacent sensors facing each other. Measure the photon collection rate and the ability to localize the location, energy, and time of arriving photons using a PET radioactivity source. These data are important for understanding the sensorís performance for PET.
4. Develop a computer simulation of the breast-dedicated PET system and realistic PET radiochemical distribution in breast tissue with spherical tumors and in the nearby heart and torso. Perform a simulated PET scan of the configuration for 30 seconds, reconstruct images that contain the tumors, and show that <1/10 inch tumors are clearly visualized with the proposed system.

The work will be done in collaboration with Dr. James Matteson at the UC San Diego Center for Astrophysics and Space Studies (CASS). The project will utilize CASS scientistís expertise in photon detection used in the field of astrophysics to assist us in developing advanced PET imaging modules that will be used to build the full system.

Final Report (2008)
Currently, there are difficulties associated with conventional breast cancer imaging methods. X-ray mammography is accepted as the best means to screen for early breast cancer. However, since x-rays often cannot penetrate through dense breast tissue and mammography cannot evaluate distorted breast tissue, 30 out of 100 screening mammography cases are inconclusive. In addition, mammography looks for small structures called calcifications, which are most often not associated with cancer, resulting in a high "false-positive" rate, meaning 80 out of 100 biopsies performed on suspicious spots seen in mammography are non-cancerous. Any scarring produced by biopsy can cause difficulties in the interpretation of future x-ray mammograms. Furthermore, doctors will often remove all the lymph nodes in the arm pit to see if breast cancer has spread, but this causes significant trauma and often yields negative results as well. Finally, there is no practical imaging technique to guide or monitor breast cancer therapy and treatments. Clearly a more specific, sensitive, and non-invasive breast cancer identification technique is needed to fill the gaps in standard methodology.

We proposed to investigate a special breast-dedicated imaging system to improve the capabilities of a medical imaging technique known as positron emission tomography (PET) that has shown promise for more accurate identification of cancer than other imaging modalities such as x-ray mammography or MRI due to its unique ability to sense and visualize increased biochemical changes in malignant compared to healthy tissue well before structural changes occur. Our basic specific aims were, first, to develop a small prototype of the system comprising four small detector sub-units, and study performance parameters relevant to PET. This part of the project we are still working on, although we have published preliminary work on this novel design. Secondly, we have mostly completed a computer simulated model of the full breast-dedicated PET system, performing simulated imaging studies with hot spheres representing tumors in breast tissue, and determining the lesion visualization/quantification capabilities.

Impact and future goals: If successful, the full proposed system will enhance PET's ability to visualize and quantify smaller breast cancer lesions. Since the final system would be small and can image the breast in close proximity, the system cost and the scan time would be reduced by about a factor of 10. These features would also enable PET to be available to smaller community-based hospitals. We hypothesize that, if successful, these factors will increase the role of PET in breast cancer management. In addition to finalizing the small prototype and studying its performance, we plan to submit a new proposal to CBCRP or another agency to fund the continued development of the system.

Current Trends in Preclinical PET System Design
Periodical:PET Clinics
Index Medicus: PET Clin
Authors: Levin CS and Zaidi H
Yr: 2007 Vol: 2 Nbr: 2 Abs: Pg:125-160

Design study of a high-resolution breast-dedicated PET system built from cadmium zinc telluride detectors
Periodical:IEEE Transactions in Nuclear Science
Index Medicus: IEEE Trans Nucl Sci
Authors: Peng H, et al., and Levin CS
Yr: 2007 Vol: M19-35 Nbr: Abs: Pg:3700-3704

Impact of high energy resolution detectors on the performance of a PET system dedicated to breast cancer imaging
Periodical:Physica Medica
Index Medicus: Phys Med
Authors: Levin CS, Foudray AM, Habte F
Yr: 2006 Vol: 21 Nbr: Suppl 1 Abs: Pg:28-34