The system development work, led by Bruno De Man at GE-Research in conjunction with Norbert J. Pelc at Stanford University, has progressed from simulations to the construction of a working proof of concept of both the multisource and the complete IGCT system.
In the future, the development team plans to scale up the experimental system from 8 to 32 sources, which will allow larger specimens to be imaged.
"The X-ray multisource and IGCT system represent a radical departure from conventional CT," says Frutschy. "Our test results show that one can construct such a system, and that it is possible to deliver a high-power x-ray multisource tube with 60kW instantaneous measured power."
The presentation "Distributed X-ray Source Development" by K Frutschy et al. will be at 1:30 p.m. on Monday, July 19 in room 201B of the Philadelphia Convention Center.
ABSTRACT: aapm/meetings/amos2/pdf/49-14518-9819-183.pdf
This research was funded by the NIH.
10) TESTING PROTON CLUSTERS
The aim of most radiation therapy methods is to kill tumors while doing as little damage as possible to surrounding healthy tissue. Beams of protons are efficient in this regard, but there are several ways of delivering protons. The conventional way is to speed them up using the same kind of electronic devices used at particle accelerators. Another is to smash laser pulses into a target, where protons are liberated not singly but in bunches. Some scientists believe that effectiveness for delivering radiation to a tumor might be superior, at least in some situations, for laser-generated proton clusters.
Eugene Fourkal and his colleagues at the Fox Chase Cancer Center in Philadelphia are performing computer simulation studies (but no clinical trials, yet) with clusters -- varying the concentration and relative spacing of the protons within clusters -- in an effort to see what works best. One practical measure of success is determining the relative biological effectiveness, or RBE, the dimensionless number showing the effectiveness of the given particle beam in killing cancer cells relative to photons (with energy 1.25 MeV) for the same physical dose level in terms of "Grays" (or Gy, the ratio of energy absorbed to the mass).
"Laser-accelerated protons are coming in a cluster," says Fourkal, "and if their concentration is high enough (inter-proton distance is small enough) the interference effects the protons encounter in the tumor may lead to higher cluster stopping power as well as a higher RBE."
The presentation "Linear Energy Transfer of Proton Clusters" by E Fourkal et al. will be at 1:30 p.m. on Sunday, July 18 in area 2 of the exhibit hall of the Philadelphia Convention Center.
ABSTRACT: aapm/meetings/amos2/pdf/49-12901-51016-247.pdf
11) SOLID-STATE X-RAY INTENSIFIERS
In traditional x-ray image intensifiers (XIIs), developed in the 1950s, X-rays, having passed through a patient's body, were converted to secondary electrons, which were accelerated by high voltages in bulky vacuum tubes. The electrons, in turn, were subsequently converted back into light, which finally was recorded by a camera. This method was used to achieve image intensification and results in distortions of the images. Although still in use, XII's began to be replaced in the 1990s by flat panel imagers, which proved to have problems of their own, such as limited spatial resolution and poor image quality for low X-ray exposures.
New solid state X-ray image intensifiers (SSXII's) based on electron-multiplying solid state sensors, developed by researchers at the University at Buffalo over the past several years, can provide superior medical imaging capabilities. The SSXII is a high-sensitivity, high resolution imager that can be operated in real-time to provide movie-like images with negligible additive electronic instrumentation noise.
Dr. Andrew Kuhls-Gilcrist of the University at Buffalo says that the next generation of SSXII devices will have an expanded field-of-view to enable larger region-of-interest imaging. "Seeing images taken with the new SSXII is like viewing high-definition TV for the first time," says Kuhls-Gilcrist. Using an extensible modular array design, the field-of-view can be expanded to larger sizes for eventual imaging of entire organs. Additional design improvements are expected to provide even greater advantages, including even finer spatial resolution and a threefold improvement in dose-efficiency at the highest spatial frequencies. Work is continuing in Dr. Stephen Rudin's imaging lab to further advance the development of this promising new technology and to bring it to the clinic, where it is expected to provide substantial improvements in patient treatment outcomes.
The presentation " The Next Generation Solid State X-Ray Image Intensifier (SSXII)" by A Kuhls-Gilcrist et al. will be at 4:50 p.m. on Wednesday, July 21 in room 201C of the Philadelphia Convention Center.
ABSTRACT: aapm/meetings/amos2/pdf/49-12777-99871-601.pdf
12) TO TREAT CANCER, SUBDIVIDE AND CONQUER
Today's cancer therapies deliver a uniform amount of radiation to the tumor as a whole. But cancer masses are not uniform throughout, and new research suggests that these treatments could be made more effective by targeting different regions of the tumor with different doses.
A comprehensive molecular imaging study lead by Robert Jeraj's group at the University of Wisconsin, Madison, showed that many tumors contain three distinct subpopulations of cells.
Thirteen patients with head and neck cancer underwent PET/CT scans that measured three different characteristics: metabolism, cell proliferation, and oxygen deprivation (hypoxia). Previous studies have shown that these three factors can vary within a tumor, and each is known to effect how a tumor reacts to treatment.
Using a computer algorithm to classify the regions based on these three parameters it was discovered that most of the tumors contained three statistically- different subpopulations with distinct profiles. He suspects that this classification into distinct tumor subregions may be generalizable to many different kinds of cancer.
Jeraj hopes to develop future therapies that up the dose given to radiation-resistant cells and drop the dose given to radiation-sensitive cells.
"There are some regions that are overtreated in a tumor and some that are undertreated," says Jeraj. "The idea is of dose painting is to treat each region properly."
One potential target for increasing the dose, said Jeraj, is the 20 percent of cells of the tumor that show high hypoxia, a low metabolic rate, and low proliferation. Candidates for a lower dose include the 30 percent of cells that show high proliferation, but low hypoxia and intermediate metabolism.
Jeraj says that future studies will be needed to identify which of these regions are more or less resistant to single a treatment, and new tools must be developed to measure how one region changes size in relationship to the tumor as a whole.
The presentation "Classification and Characterization of Tumor Subpopulations Using Molecular Imaging" by R Jeraj et al. will be at 1:30 p.m. on Monday, July 19 in room 204B of the Philadelphia Convention Center.
ABSTRACT: aapm/meetings/amos2/pdf/49-12978-36242-62.pdf
13) RED-FLAGGING CANCER
In recent years, nanoparticles have shown promise for detecting and imaging tumors. At the Stanford University School of Medicine in California, an interdisciplinary group of researchers has developed a range of nanocrystals that work with X-rays to light up cancer cells with a red glow.
Their technique, called X-ray luminescence computed tomography, could see smaller cancerous lesions with less radiation dosage than current technologies used to image biological processes in the body -- such as PET/CT scans.
The nanocrystals created by Guillem Pratx and his colleagues produce infrared light when exposed to X-rays. The researchers hope to coat the crystals with polymers and proteins that would enable them to circulate through the human body and attach to cancer cells. Radiation from a CT scanner could then light them up, and this light -- generally harmless to the human body -- would be detected by a simple CCD camera.
Because infrared light tends to be absorbed by the body, these crystals may one day be most useful in a clinical setting for imaging shallow tissues or for organs that can be reached with a fiber optic cable that can detect the light.
"If light is not coming out of the subject, if the tissue is deep, you could go in with an endoscope to detect it," said Pratx. "You could possibly use this for prostate or colorectal cancer imaging."
Pratx has successfully detected the crystals inside of 6-centimeter gelatin cylinders that have optical and X-ray properties similar to those of human tissue, and in cervical cancer cells in a petri dish.
The researchers are now beginning to test the toxicity and effectiveness of these crystals in mice.
The presentation "X-Ray Luminescence Computed Tomography Via Selective X-Ray Excitation" by G Pratx et al. will be at 4:00 p.m. on Monday, July 19 in room 204C of the Philadelphia Convention Center.
ABSTRACT: aapm/meetings/amos2/pdf/49-13905-2259-485.pdf
14) MORE MEETING INFORMATION
The presentations at the AAPM meeting will cover topics ranging from new ways of imaging the human body to the latest clinical developments on treating cancer with high energy X-rays and electrons from accelerators, brachytherapy with radioactive sources, and protons. Many of the talks and posters are focused on patient safety -- tailoring therapy to the specific needs of people undergoing treatment, such as shaping emissions to conform to tumors, or finding ways to image children safely at lower radiation exposures while maintaining good image quality.
RELATED LINKS
- Main Meeting Web site: aapm/meetings/2010AM
- Meeting program:
aapm/meetings/2010AM/MeetingProgram.asp
- AAPM home page: aapm
SOURCE American Association of Physicists in Medicine