Toward a compact microbeam radiotherapy system

Toward a compact microbeam radiotherapy system. The intense, narrow x-ray beams produced by synchrotrons are ideal for zapping tumors: With diameters of just 10–100 μm, the beams deliver a dose pattern with exquisite precision. What’s more, for some unknown reason, the beams’ high intensity is both more effective at killing tumors and less damaging to healthy tissue than are the lower-intensity beams used in conventional radiotherapy. But synchrotrons are large, expensive, and sparsely distributed. To circumvent those disadvantages, Sha Chang and Otto Zhou of the University of North Carolina in Chapel Hill are developing a compact, convenient method for bringing what’s known as microbeam radiotherapy into the clinic. Their approach entails producing x rays by slamming high-energy electrons into a tungsten anode, just as in dental cameras and other medical x-ray devices. But instead of boiling off the electrons from a metal cathode, they use the field effect to extract the electrons from a cathode made from carbon nanotubes. Thanks to the nanotubes’ tiny diameters, the resulting x-ray beams, while not as powerful as those from synchrotrons, are almost as narrow. To assess whether the technology is practical, Chang and her colleague Eric Schreiber simulated a device capable of treating lab mice. The virtual device consists of a circular array of 12 or more units that direct their beams inward toward the circle’s center. As they report in a new paper, the device can indeed deliver a tumor-killing dose to tightly defined volumes within a phantom mouse. The researchers are now testing their first prototype. (E. C. Schreiber, S. X. Chang, Med. Phys. 39, 4669, 2012.)