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BURIED AMMONOID: As viewed through megavoltage computerized tomography (CT), a 370-million-year-old ammonoid from the Devonian period, an extinct cephalopod relative of squids, octopuses and the chambered nautilus. Ammonoids died out around the same time as dinosaurs, about 65 million years ago, at the Cretaceous–Tertiary (K–T) extinction event. The TomoTherapy machine's four-million-electron-volt x-rays are energetic enough to penetrate rock, as this image reveals.
Courtesy of James Welsh and the University of Wisconsin Cancer Center-Riverview

Using a novel radiotherapy technology called helical tomotherapy—in essence, the marriage of a computerized tomography (CT) scanner and a radiotherapy linear accelerator—James Welsh, associate professor of medical physics and human oncology at the University of Wisconsin School of Medicine and Public Health, and a group of colleagues have created images of fossil specimens of various types and ages.

TomoTherapy, Inc.'s Hi-Art radiation machine, developed at the University of Wisconsin–Madison, is designed to treat cancer patients with intensity-modulated radiation therapy (IMRT). The CT component provides images of tumor position right before each daily treatment session so that doctors can target malignancies while avoiding healthy cells. The Hi-Art device is designed to rotate around a patient, delivering narrow, potent and precise doses of radiation to tumors without harming healthy tissue nearby—a process that takes 15 to 25 minutes. "I was fortunate to be the first MD to ever treat a patient with this technology," Welsh says. "I suspect these are the world's first megavoltage CT images of rocks and fossils from such a unit."

The use of image-guided IMRT technology has shown promise in treating cancer, and TomoTherapy is expected to soon have competitors. Sharp Grossmont Hospital in La Mesa, Calif., offers patients access to a Hi-Art system, but there are only about 30 medical facilities in the country using helical tomotherapy. This is expected to change after Varian Medical Systems, Inc., in Palo Alto, Calif., gets Food and Drug Administration approval to sell its RapidArc IMRT system. Elekta, AB, in Sweden also offers comparable image-guided radiation therapy technology.

Research is currently being conducted on other possible uses for these devices. "I plan to obtain more images and continue a scientific evaluation of the potential of this clinical machine for paleontological and geological purposes," Welsh says. "I expect a peer-reviewed manuscript will be ready by midyear."