Number 833, July 23, 2007
by Phil Schewe and Ben Stein
Ultrasound Warning Signal for Breast Cancer
Studies by scientists at the Karmanos Cancer Institute and Wayne State University have discovered a correlation between the speed of ultrasound transmitted through breast tissue and the density of that tissue. This is potentially important because high amounts of dense breast tissue are associated with increased
breast cancer risk.
Using ultrasound avoids the use of ionizing x-rays used in typical mammography. The researchers are part of a team that has been developing a new form of performing ultrasound tomography, one in which the patient is in the prone position, with a breast projecting down into a bath of water. The breast is surrounded by a ring-shaped transducer for sending and collecting sound waves into the breast from all sides.
The resulting
ultrasound detection captures both reflected and transmitted sound waves. From this, an ultrasound percent density (USPD)-thought to be a good proxy for mammographic density-can be determined. The method has been tried out in a clinical trial with a cohort of 100 patients and shows that USPD corresponds well with both qualitative and quantitative mammographic breast density measures.
These results are being reported next week at the meeting of the American Association of Physicists in Medicine (AAPM) in Minneapolis. One of the scientists, Carri Glide (glidec@karmanos.org), says that they hope to gain FDA approval and introduce the device into general use. Further information about the device can be found at www.karmanos.org/cure. (AAPM meeting information at http://www.aapm.org/meetings/07AM/VirtualPressRoom/generalrelease.asp)
Miniaturizing Proton Therapy
Using innovative physics, researchers have proposed a system that may one day bring proton therapy, a state-of-the-art cancer treatment method currently available only at a handful of centers, to radiation treatment centers and cancer patients everywhere. Compared to the x rays conventionally used in radiation therapy, protons are potentially more effective, as they can deposit more cell-killing energy in their tumor targets and less in surrounding healthy tissue.
However, to kill tumors, the protons must be accelerated to sufficiently high energies, which currently must be achieved in large, expensive accelerators occupying spaces the size of basketball courts. Thomas Mackie (trmackie@facstaff.wisc.edu), a professor at the University of Wisconsin and co-founder of the radiation therapy company TomoTherapy, will speak at the AAPM meeting, where he will present a proton-therapy design based on a much smaller device known as a "dielectric wall accelerator" (DWA).
Currently being built as a prototype at Lawrence Livermore National Laboratory, the DWA can accelerate protons to up to 100 million electron volts in just a meter. A two-meter DWA could potentially supply protons of sufficiently high energy to treat all tumors, including those buried deep in the body, while fitting in a conventional radiation treatment room.
The DWA is a hollow tube whose walls consist of a very good insulator (a dielectric). When most of the air is removed from the tube to create a vacuum, the tube can structurally withstand the very high electric-field gradations necessary for accelerating protons to high energies in a short distance.
In addition to its smaller size, a DWA-based proton therapy system would have another benefit: it could vary both proton energy and proton-beam intensity, two variables that cannot both be adjusted at the same time in existing proton-treatment facilities.
Mackie cautions that clinical trials of the system are at least five years away. But if the DWA approach proves feasible, protons may eventually represent a widespread, rather than limited, option for treating cancer. (AAPM Paper TH-C-AUD-9.)
A Solid State X-Ray Image Intensifier (SSXII)
A solid state x-ray intensifier (SSXII), now in development, should greatly improve the spatial resolution of medical x-ray imaging. In angiography (imaging blood vessels using higher x-ray exposures to provide a very high-quality, low noise diagnostic image) and fluoroscopy (real-time imaging at lower x-ray exposures for image guidance) it is important to minimize the x-ray dose to the patient and to maximize the sensitivity of the detectors recording the image.
Usually an x-ray image intensifier (XII) or a flat panel detector (FPD) is employed. These are devices used for converting the x-ray image into a digital image. The XII suffers from inherent image distortions due to the method of image intensification including susceptibility to the earth’s magnetic field.
As a result, the XII is currently being replaced by the newer FPDs which overcome these distortion problems. Unfortunately the flat panel detectors themselves suffer from excessive instrumentation noise, resulting in poor image quality at the lower x-ray exposures required for fluoroscopy. Both detectors have limited spatial resolution.
Now, scientists at the University at Buffalo are developing a solid state version of the traditional x-ray image intensifier, one which relies upon electron multiplying CCDs to provide variable signal amplification in solid-state. The result should be a device which incorporates all the positive features of current state-of-the-art fluoroscopic imagers, but with minimal image distortions unaffected by magnetic fields, extremely low instrumentation noise, variable sensitivity down to very low x-ray exposures, and more than double the spatial resolution.
Andrew Kuhls (atkuhls@buffalo.edu, 716-829-3595 x114), working in Professor Stephen Rudin’s medical imaging physics group, says that in-vivo testing of the new device is planned, with clinical trials to follow. (Three talks at the AAPM meeting: WE-C-L 100J-3, 2007, WE-C-L 100J-4, 2007, WE-C-L 100J-6, 2007)
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