Genetic radiotherapy, PET scans for animals, novel spinal surgery

July 08, 2002

College Park, MD, 3 July 2002 - Montreal will host the 44th annual meeting of the American Association of Physicists in Medicine (AAPM) July 14-18, 2002 at the Palais des Congrès de Montréal. The meeting will feature some of the latest and most important developments in medical imaging and radiotherapy.

Introduction

Ever since the discovery of x-rays and their potential for medical imaging, physicists have been vital to the advancement of medicine. Fundamental research in optics, acoustics, electromagnetism, and particle and nuclear physics have led to an array of indispensable medical tools. Magnetic resonance images, CAT scans, PET scans, and various types of radiotherapy are among the physics-based devices that help doctors diagnose and treat ailments ranging from broken bones to cancer. Ultrasound machines, for example, are made possible through our understanding of the physics of sound waves, and the prenatal images they produce are now so common that they are a cultural symbol of the joy of impending parenthood. Cutting-edge techniques presented in the annual AAPM meeting scientific program will ultimately lead to tools as important to the medicine of tomorrow as x-ray and ultrasound images are today.

The AAPM includes more than 4500 members dedicated to advancing medical technology. Medical physicists contribute to the effectiveness of radiological imaging procedures by assuring radiation safety and helping to develop improved medical imaging. They also develop therapeutic techniques (such as prostate implants and stereotactic radiosurgery)and collaborate with radiation oncologists to design treatment plans. Medical physicists working in radiation therapy commission, calibrate, and model therapeutic equipment to ensure that every patient receives precisely the prescribed dose of radiation at the correct location.

Highlights of the scientific program

The following is a sampling of some of the intriguing talks that medical physicists will present at the 44th Annual AAPM meeting.

Increasing cancer cures with genetic radiography

Genetic radiotherapy, an innovative marriage of gene therapy and radiation therapy, can increase cancer cure rates by significant amounts compared to the cure rates offered by radiation treatment alone, a Virginia Commonwealth University team of medical physicists has concluded (Paul Keall, pjkeall@vcu.edu). In genetic radiotherapy, cancer cells are infected with a virus that makes these cells more sensitive to--and more easily destroyed by--radiation such as x rays. The technique is currently evolving from laboratory studies to clinical trials. Incorporating human patient data from large clinical trials as well as experimental data from laboratory work, the Virginia Commonwealth researchers will present a quantitative model predicting the increase in cancer cure rates with genetic radiotherapy.

Analyzing presently achievable laboratory capabilities, the researchers predict an increase in cure rate of 15% when genetic radiotherapy is used instead of conventional radiation treatments on non-genetically-altered cancer cells. Exploring an ideal situation in which all of the cancer cells are genetically modified, they find the technique can theoretically increase the cancer cure rate by as much as 70%. Thus, their results indicate that genetic radiotherapy has the potential to significantly improve cancer cure rates compared to current radiotherapy practices. (Paper MO-E-517B-7, Monday, 4:00 PM).

Pet for animals.

The course of health or illness or drug response in rats and mice is an important part of medical research. But getting a high-precision, inside look at these small animals, through positron emission tomography (PET), is difficult because the spatial resolution of clinical PET (4-6 mm) and the radiotracer sensitivity are not good enough for looking at such small organs, especially if one wants to watch medical effects in real time. Medical physicists at the University of Sherbrooke in Canada have now achieved the needed improvements, partly by using faster radiochemistry techniques in monitoring the uptake of tracers during metabolism; but the major improvement was gained by replacing the old photomultiplier tubes (used to look for telltale radiation from positron-electron annihilation) with solid state avalanche photodiodes. Now, for example, the precision in cardiac studies in rats can match that achieved with humans in current clinical scanners. Furthermore, Roger Lecomte (rlecomte@courrier.usherb.ca) reports at the AAPM meeting that he and his colleagues are developing what he expects to be the first dual modality PET/CT scanner using the same detection system for molecular and anatomic imaging. This will, among other innovations, permit the use of radiotracers which offer a more targeted analysis of specific tissues. (TH-C-519-6, Thursday, 11:00 AM).

Closing in on strokes with high resolution imaging

A new, high-resolution imaging system may soon give neurosurgeons unprecedented access to the aneurysms and blood vessel constrictions in the brain that often lead to stroke. Iacovos Kyprianou (kypriano@buffulo.edu) and colleagues at the Toshiba Stroke Research Center of the University of Buffalo have developed a Region of Interest (ROI) microangiography system that provides high resolution, real-time, x-ray images of brain in areas only 5 centimeters across. ROI images allow surgeons to insert and manipulate tiny devices to directly treat diseased or damaged blood vessels. Customized ROI systems will ultimately help in the treatment of complex cases that are currently beyond the scope of surgical technology. In addition, high resolution imaging may offer us a better understanding of blood flow in the brain, and lead to less invasive therapies for stroke and other neurovascular diseases.(WE-D-518-7, Wednesday, 2:42 PM)

New faster treatment for spinal tumors - Spinal radiosurgery

Using intensity-modulated and image-guided techniques, researchers and medical staff at Henry Ford Hospital Systems in Detroit have, for the first time, been able to treat over 40 patients with spinal indications/cord compression in a single session of radiation treatment while minimizing radiation exposure to critical organs such as the spinal cord. Current treatment methods for spinal tumors require multiple treatment visits for the patients, who must often wait several weeks to see a reduction in pain and discomfort from the tumor. With this new technique, medical physicists Dr. Fang-Fang Yin (fyin1@hfhs.org) says only one treatment session is needed and pain relief and function improvements occur within two weeks. With this technique, the radiation dose the spinal cord receives is much smaller than the dose given to the tumor, allowing for higher doses of radiation in a single session. Dr. Yin and his colleagues believe this treatment method will become a standard treatment procedure that will improve the quality of patient care and potentially reduce treatment costs. (TH-C 517B-6, Thursday, 10:50 AM).

Ultrasound advance for osteoporosis and bone imaging

Medical physicsists will report on an ultrasound technique that, with further development, could have a significant impact on the diagnosis and treatment of osteoporosis, the thinning and loss of elasticity of bone that eventually affects everyone in advanced age. In a collaboration between California State University-Dominguez Hills (CSUDH), the University of Florida, UCLA Medical Center, and Second Wave Systems Corp. in Pennsylvania, researchers showed that ultrasound works almost as well as an x ray to determine the mineral density of a bonelike material (a careful blend of bone ash and petroleum jelly). If successfully developed into a clinical system for human patients, routine ultrasound bone tests might be made in the future without subjecting people to the anxiety and minimal damage of receiving a small dose of radiation.

In a second result, the researchers have shown that high frequency ultrasound (200 kHz to 2 MHz) can be transmitted through skin, tissue, and bone without any contact with the patient. To achieve this difficult feat, the researchers combined a highly sensitive ultrasound detector with an acoustic-wave transducer that sends sound through a series of specially designed layers to transmit ultrasound efficiently from air to a solid such as bone. The researchers' ultrasound scanner could be used like an x-ray machine with a standard scanning motion and without the need for a clinician to apply messy gels and run an ultrasound wand over the patient's body. Such X-ray-like ultrasound check-ups, if realized, could find widespread use among tens of millions of Americans and others who are concerned about aging bones or osteoporosis. Also, such a technique might enable more frequent monitoring of astronauts, for example, on extended stays at the International Space Station, who face an increased risk of losing bone mass and developing bone brittleness. (MO-D-519-5, Monday, 2:25 PM; contact Mahesh C. Bhardwaj, SecondWave Systems, 1-814-466-6200, Mcbhardwaj@aol.com, www.secondwavesystems.com, Kenneth Ganezer, California State University-Dominguez Hills, 310- 243-3438, kganezer@csudh.edu)

GAMMA KNIFE is the name for a machine in which high energy gamma-rays are used to irradiate intracranial tumor cells difficult to treat with other methods. Acoustic neuroma, a tumor lodged in the vestibular nerve, is an example. In the Boston Gamma Knife Center of Jen-San Tsai, Ph.D., at Tufts New England Medical Center of Boston an array of 201 gamma-emitting cobalt-60 sources is laid out in such a way that the rays converge on the target tumor, whose coordinates are carefully determined by CT and MRI scans. The resultant noninvasive procedure, called stereotactic radiosurgery, is in use at 66 facilities in North America, and 154 facilities installed worldwide. At the AAPM meeting, Dr. Tsai (jtsai@lifespan.org, 617-636-1681) is reporting new methods for coordinating MRI and CT scans to obtain the best possible tumor location to insure proper dosages.(TH-C-517B-7, Thursday, 11:00 AM)

Early detection of breast cancer may be aided by new insight into tissue's mechanical properties

In work that may aid a promising approach for detecting breast cancer earlier, researchers at Dartmouth-Hitchcock Medical Center and Dartmouth College (John B. Weaver, 603-650-7230, john.b.weaver@hitchcock.org) have made a new discovery in the mechanical properties of breast tissue. Breast cancer remains the most commonly detected cancer in women. In efforts to reduce the deadliness of this disease, several groups of researchers worldwide are developing magnetic resonance (MR) elastography, a recent innovation in magnetic resonance imaging, to help diagnose breast cancer earlier and more accurately. Elastography measures the stiffness of tissue in the body.

However, before MR elastography can become a reliable early detection tool for this deadly cancer, researchers must fully understand breast tissue's mechanical stiffness properties--and these properties are proving to be surprisingly complex. The Dartmouth-Hitchcock team has shown for the first time that some normal, noncancerous breast tissue may be anisotropic, that is, its stiffness is different depending on in which direction it is pushed and pulled. Rope or string provides a classic example; it is very difficult to stretch rope lengthwise but easy to move it perpendicular to its length. In studies of two human subjects, the researchers found most tissue within the breasts to be isotropic but they also detected regions that were clearly anisotropic.

The preliminary results suggest that the presence of anisotropic tissue is not in and of itself indicative of breast cancer, as an earlier study by other researchers had suggested. The researchers' results and experimental techniques provide a way to elucidate the important mechanical properties of the tissue and aid efforts to develop MR elastography into a powerful early breast cancer detection tool. (MO-D-518-6, Monday, 1:30 PM)

New advance for measuring radiation doses in real time

Researchers from Risoe National Laboratory in Denmark, Malmoe University Hospital in Sweden, Oklahoma State University and Landauer Inc. are reporting on a new optical fiber in-vivo dosimetry system. This device allows the monitoring of the amount of radiation received by a patient in real time with significant improvements regarding tissue equivalence and stability. The new system monitors optical stimulated luminescence (OSL), which is directly related to the amount of absorbed radiation, and radioluminescence (RL), which reflects the dose rate or the strength of the treatment given over a period of time. The system uses a single optical fiber which can be placed on the body surface or in cavities near organs of interest. The researchers say this dosimetry system will improve the flexibility and accuracy in radiotherapy, resulting in physicians and technicians who can better control tumor radiation with fewer side effects. (contact: Marianne Aznar, Marianne.aznar@risoe.dk) (TH-C-517D-8, Thursday, 11:10 AM).

These items were prepared by James Riordon, Phil Schewe, Rory Richards, and Ben Stein of the American Institute of Physics in cooperation with the American Association of Physicists in Medicine and the respective speakers.




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