Research on a Novel Cancer Diagnosis and Therapy Machine
A multidisciplinary team of University physicists, engineers，biologists, and radiologists headed by the University of California at Davis, and including Stanford Linear Accelerator Center and UCLA, is developing a source of tunable, monochromatic x-rays, suitable for the diagnosis and treatment of cancer in hospitals. The x-ray source (CXS) is based on Compton backscattering of a high peak power, short pulse laser beam off energetic electrons from a linear accelerator, producing x-rays that are tunable between 20 and 100 keV by changing the energy of the electron beam.
The CXS source is being assembled at the Stanford Linear Accelerator Center (see for SLAC facilities), and uses much of the X-band photoinjector technology developed there for high-energy physics research, which has the highest gradient ever produced in an RF gun. Companion projects to the CXS are conducting research on a variety of nanodevices (microplatforms, see for example), capable of being targeted to cancerous lesions in a patient, and being triggered to deliver drugs, or to carry contrast agents useful in radiography.
The CXS machine under development at SLAC is being designed for cancer detection and therapy, in conjunction with these nanoplatforms as indicated in the schematic representation below. Tunable, monochromatic CXS x-rays are used to communicate with targeted nanoplatforms in the vicinity of cancer cells by interacting with high-Z (high atomic numbers like indium, iodine, gadolinium, gold, platinum) materials attached to the nanoplatforms. The x-rays excite the K-shell of the metal, releasing low energy electrons and secondary x-rays that attack the DNA in cancer cells in the case of therapy or interact with the materials to provide a high resolution detection and monitoring capability in the case of imaging.
The projected use of the CXS x-ray source can best be considered by the futuristic breast cancer diagnosis and treatment scenario here. The corresponding conventional scenario would involve surgical intervention in both the diagnosis and treatment phases.
Ongoing Research Activities:
CXS is under development and the commissioning of the system is expected soon.
X-Ray Phototherapy Research:
We are employing Synchrotron Radiation (SR) monochromatic x-rays at SSRL, APS, and ALS, as well as the conventional polychromatic x-rays at UC Davis Medical Center, to carry out in vitro human cell radiosensitization experiments with different contrast agents like indium, iodine, gadolinium and gold. In these studies cultured cells immersed in solution of contrast agents, or with the contrast agents directly targeted in the nucleus, are irradiated with different energies of monochromatic x-rays below and above the k-edge of the agents, or with optimized kVp in the case of polychromatic x-rays, to study the dose enhancement effects of the contrast agents under different concentrations.
Animal model may also be constructed later to carry out in vivo studies.
Given the spread of the conventional x-ray energy spectrum, the low energy portion photons could not penetrate and thus add entry dose without helping the imaging; on the other hand, the high energy photons have very high penetration thus decrease the contrast and degrade the image. And this uneven attenuation of photons with different energies is accordingly called beam hardening since the beam becomes harder with filtration. So by using monoenergetic x-ray offered by CXS, we can get better image with lower dose.The figure of merit is calculated out and possible new techniques like contrast enhanced imaging and dual-energy subtraction imaging are explored.
source spot size of CXS is in tens of microns range, much finer than the
millimeter range of the conventional x-rays, so that the “optical biopsy”,
in which the fine image of the lesion can be formed using
For more information, please browse the following CLS overview files.
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