Faster Tracking of Lung Tumors May Help Treatment
FOR IMMEDIATE RELEASE
For more information, please contact:
Jason Socrates Bardi,
American Institute of Physics,
Sudarshan Chamakuri, , Ph.D., DABR
AAPM Media Relations Subcommittee Chair
PHILADELPHIA, PA (July 20, 2010) -- Today, at the 52nd Annual Meeting of the American Association of Physicists in Medicine (AAPM) in Philadelphia, a group of researchers from Stanford University will describe the latest developments toward their goal of integrating two existing medical devices -- medical linear accelerators, or "linacs," which produce powerful X-rays for treating cancer, and magnetic resonance imagers (MRIs), which are widely used to image tumors in the human body.
The new research involves trying to significantly increase the speed of MRI imaging using a concept called "spatio-temporal sparsity," which traces its origins to video compression and streaming Web movies. By using it on medical MRI images, the Stanford team managed to triple their image acquisition speed -- fast enough to acquire 2D and 3D images of lung tumors in real time as they move with a patient's every breath.
This faster speed allowed the team to visualize tumor tissue itself in real time inside two human patients -- just fast enough and at sufficient resolution to guide treatment. And they believe that they can improve on this further.
With these new results and the hardware integration work done to date by other groups in this field, Amit Sawant, a researcher in the Department of Radiation Oncology at Stanford University who led this research, says that the first prototype hybrid Linac-MR system may be available within a year. He adds, however, that clinical trials and federal regulatory approval of clinical protocols are expected to take a few more years.
IMAGING TUMORS IN MOTION
The success of modern radiation therapy often depends on how well doctors can determine the exact location and shape of a tumor based on a set of images. Imaging techniques have improved to the point that doctors can now define the edges of many tumors to within a fraction of an inch. During treatment, however, many tumors will move. Tumors in the lungs, for instance, can move up to an inch or more as a person breathes.
In recent years, a variety of imaging techniques have emerged for guiding radiation treatment, and two approaches have typically been used to guide radiation therapy delivery to tumors in the lung and abdomen. The first, the use of external "surrogate" markers placed on the chest wall, suffers from the assumption that a tumor inside the lung will move more or less in sync with chest contraction and expansion during breathing. The second approach makes use of internal surrogates, dense gold seeds implanted into either lung bronchi or the tumor itself, that define the tumor location based on X-ray images. But neither of these approaches gives true image-based guidance of the entire volume of the tumor, says Sawant.
A hybrid Linac-MR system, however, would allow doctors to accurately monitor moving tumors in a patient's lungs and other soft tissues such as the liver or prostate in real time at a resolution and speed that would allow effective guidance of radiation therapy while the treatment is ongoing. Last year, a group in Canada overcame many of the technical hurdles to building such a device and demonstrated the first operating prototype Linac-MR system.
Now Sawant and his Stanford colleagues Kim Butts Pauly and Paul Keall have made another important contribution to the development of this technology, which Sawant and his student Cheol Pyo Hong will present in Philadelphia this week.
THE NEED FOR SPEED
The problem they were addressing is one that may be known to anyone who has had an MRI scan -- the machines are slow. Typical imaging times for MRI range from several seconds to a few minutes per image, which is not fast enough to track tumors in motion.
"What we need is 10 times that speed if we want to be confident we are capturing the motion," says Sawant. Now they are a closer to that goal.
Rather than sampling the entire tumor and processing all that data in real time, they developed an imaging technique that calculates the difference between successive images. Human anatomy and the shape of a tumor don't change radically from image to image, says Sawant, explaining "We only need to image what HAS changed."
By selecting only for changes in successive images, they can streamline the scanning process by close to 70 percent -- essentially cutting the time needed to obtain each image to less than one-third.
"This was an initial investigation," says Sawant. "With clever reconstruction schemes, you could further increase the imaging speed probably by a factor of 10."
The presentation "Real-Time MRI for Soft-Tissue-Based IGRT of Moving and Deforming Lung Tumors" by A Sawant et al. will be at 10:00 a.m. on Wednesday, July in room 204B of the Philadelphia Convention Center. READ THE ABSTRACT
The presentation "Rapid MR Imaging for Real-Time Target Tracking Using Temporal Sparsity" by C Hong et al. will be at 1:30 p.m. on Tuesday, July 10 in room 204B of the Philadelphia Convention Center.
MORE MEETING INFORMATION
AAPM is the premier organization in medical physics, a broadly-based scientific and professional discipline encompassing physics principles and applications in medicine and biology. Its membership includes medical physicists who specialize in research that develops cutting-edge technologies and board-certified clinical medical physicists who apply these technologies in community hospitals, clinics, and academic medical centers.
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.
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Press registration on-site will take place at the AAPM Registration Desk, 200 Level Bridge just outside Hall A-B in the Pennsylvania Convention Center.
Questions about the meeting or requests for interviews, images, or background information should be directed to Jason Bardi (firstname.lastname@example.org, 858-775-4080).
ABOUT MEDICAL PHYSICISTS
If you ever had a mammogram, an ultrasound, an X-ray, CT, MRI or a PET scan, chances are reasonable that a medical physicist was working behind the scenes to make sure the imaging procedure was as effective as possible. Medical physicists help to develop new imaging techniques, improve existing ones, and assure the safety of radiation used in medical procedures in radiology, radiation oncology and nuclear medicine. They collaborate with radiation oncologists to design cancer treatment plans. They provide routine quality assurance and quality control on radiation equipment and procedures to ensure that cancer patients receive the prescribed dose of radiation to the correct location. They also contribute to the development of physics intensive therapeutic techniques, such as the stereotactic radiosurgery and prostate seed implants for cancer to name a few. The annual AAPM meeting is a great resource, providing guidance to physicists to implement the latest and greatest technology in a community hospital close to you.
The AAPM is a scientific, educational, and professional nonprofit organization whose mission is to advance the science, education and professional practice of medical physics. The Association encourages innovative research and development, helps disseminate scientific and technical information, fosters the education and professional development of medical physicists, and promotes the highest quality medical services for patients. Please visit the Association Web site at http://www.aapm.org/