Development of the Lampshade Compton Camera for Medicine

The collimator that is used in today's SPECT scanners limits the energy of the isotopes that can be imaged. With the advancements that will be achieved in this research, I believe that a lampshade Compton camera will be able to make medically useful images in the range of 0.3 MeV to 3.0 MeV. This ability could lead to a number of significant advancements in medicine; perhaps, the following is the timeliest.

Improve the imaging capabilities of image-guided targeted radionuclide therapy

The ideal cancer therapy would destroy all cancerous cells without damaging noncancerous cells. It is hoped that a new therapy, called targeted radionuclide therapy, will perform more ideally than the conventional chemo and radiation therapies. With conventional chemotherapy, all rapidly dividing cells, whether they are cancerous or not, are targeted for destruction. In contrast, with targeted radionuclide therapy, a molecule labeled with a radionuclide is used to deliver radiation to just the cancerous region.

The advantage of targeted radionuclide therapy over conventional radiation therapy is illustrated in the figure below. As illustrated on the left in the figure, with conventional radiation therapy the radiation emanates from a source outside the patient and is focused on the cancerous region. Unfortunately, it is seen that non-cancerous regions receive radiation as well. In contrast, with targeted radionuclide therapy, which is illustrated on the right in the figure, only the cells near the cancerous regions receive the radiation.

The FDA has approved two radiopharmaceuticals—yttrium-90-ibritumomab tiuxetan (Zevalin) and iodine-131-tositumomab (Bexxar)—that can be used in targeted radionuclide therapy. Neither of these radiopharmaceuticals can be effectively imaged with today’s nuclear imaging devices (SPECT and PET scanners). However, I expect that the lampshade Compton camera will be able to image both of them.

Comparison of Cancer therapies. Taken from Advancing Nuclear Medicine Through Innovation by the National Research Council and Institute of Medicine, 2007.

Data collection geometry: the key to improving SPECT

For over thirty years, Compton cameras have been investigated for use in medicine. To date, there as been only one successful application of Compton cameras—the Comptel telescope, I believe the principal reason for the lack of success of Compton cameras is the data collection geometry used in the cameras.

The conventional camera design consists of two parallel planar detectors. The data produced by a Compton camera can be modeled as being an integral of the distribution of radioactivity within the patient over a cone. The axes of symmetry of the cones associated with the data that can be measured in this design, are largely perpendicular to the face of the detector. I believe that the lack of success of Compton cameras is principally due to the data collection geometry associated with this design.

When a new data collection geometry is used, I believe that Compton cameras will be able to achieve significant advancements in medicine. In contrast with the conventional geometry, when the new geometry is used, the axes associated with the data are largely parallel to the face of the detector. This data collection geometry motivated the novel design of the lampshade Compton camera. An objective of my research is to demonstrate that the data collection geometry used in a lampshade camera is superior to the conventional data collection geometry.