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© Newswise.
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Science Highlights of the 50th AAPM Meeting in Houston, July 27 to July 31
Newswise — Whether X-rays for CT scans, sound waves for ultrasound, magnetic fields for MRI, or antimatter for PET scans, the "stuff" of physics has revolutionized the practice of medicine. In the last half century, the field of medical physics has emerged thanks to the efforts of scientists who develop these technologies and bring them to the clinic. Almost all the hospitals in the United States today benefit from the work of medical physicists. They help diagnose illness by designing and implementing new and better ways of imaging the human body. They create treatment strategies for fighting cancer and other diseases. They take measures to ensure the safety of millions of people in the United States each year who undergoing these treatments. Next week, thousands of medical physicists will meet at the 50th meeting of the American Association of Physicists in Medicine (AAPM) from July 27 to July 31 in Houston, Texas. AAPM is the largest association of medical physicists in the world. "Traditionally our annual meeting is where scientists and clinicians working on the cutting edge of medical imaging and cancer therapy come to sharpen their knives, says AAPM President Gerald A. White, M.S., FAAPM, FACR. "This year's meeting in Houston is on track to be the largest and most important in the history of the AAPM. The organization was founded in the dawn of the atomic age, and each year our members build on that heritage to investigate and implement scientific and technological innovations that give definition to the medical care of the future." Journalists are invited to cover the AAPM meeting in person or remotely. In the coming days, additional news releases will detail additional meeting highlights. All news releases will be hosted on the AAPM website (see link below). -----SECTION ONE: HIGHLIGHTS IN BRIEF----- 1) GOLD NANOSHELLS HELP VISIBLY HEAT AND DESTROY CANCER 2) TRACKING STEM CELLS TO THE HEART 3) NEW IRRADIATION METHOD HOLDS POTENTIAL FOR IMPROVING BONE MARROW TRANSPLANT PRECONDITIONING STEP 4) ATTACKING TUMORS BIT BY BIT 5) NEW RADIATION THERAPY METHOD OFFERS SHORTER TREATMENT TIME 6) TUNING X RAYS FOR THERAPY AND IMAGING 7) COMPUTER-AIDED ORGAN IDENTIFICATION 8) NEW TECHNIQUE TO ESTIMATE LUNG TUMOR CHANGES 9) HOSPITAL COMPILES EXPERIENCE WITH LATEST IMAGE-GUIDED RADIATION THERAPY 10) CELEBRATING 50 YEARS OF WOMEN IN MEDICAL PHYSICS 11) PREVENTING MEDICAL ERRORS IN RADIATION THERAPY -------SECTION TWO: FULL DETAILS ON SELECTED HIGHLIGHTS------ 1) GOLD NANOSHELLS HELP VISIBLY HEAT AND DESTROY CANCER To overcome these treatment limits, a group of researchers based at the University of Texas' M.D. Anderson Cancer Center, turned to lasers and nanotechnology. They explored an emerging minimally-invasive approach to treating tumors that delivers a lethal dose of laser-generated heat to tumors, known as thermal ablation. To improve thermal ablation, they added a nano-twist that precisely guides and concentrates heat in targeted tumors. Working with Nanospectra Biosciences, Inc., researchers injected nanoshells made of gold silica into canine models of brain cancer. The nanoshells homed to the target tumors, where they were taken in by the tumor cells. Next, researchers irradiated the nanoparticle-filled tumor with low-power laser light to selectively heat the tumor-but not the surrounding, healthy tissue. M.D. Anderson researchers added iron-oxide cores to the nanoshells to make them visible by magnetic resonance imaging so researchers could observe the process. Results from these experiments were supported by numerical modeling studies, and by scanning electron microscope data showing destructive thermal increases near the tumors’ blood supplies. "Based on these encouraging early results, we conclude that the use of magnetic resonance temperature imaging and gold nanoshells hold the very real possibility of meeting the long-sought goal of improving the precision of thermal ablation, while sparing healthy tissue," explains M.D. Anderson Cancer Center’s R.J. Stafford, Ph.D. . “Temperature imaging and guidance is an invaluable tool furthering this approach as it moves from feasibility studies to future use in human clinical trials." Talk (WE-C-351-1), "Characterization of Gold Nanoshells for Thermal Therapy Using MRI" is at 10:00 a.m. on Wednesday, July 30, 2008 in room 351. 2) TRACKING STEM CELLS TO THE HEART Mesenchymal stem cells, or MSCs, are found in the bone marrow and can differentiate into certain cell types. They have been detected around heart injuries following a myocardial infarction (heart attack), but whether they come to regenerate heart tissue or to promote healing is still under debate. Using a series of MRI scans, Tom Hu and colleagues at the Medical College of Georgia in Augusta, GA, have tracked MSCs in a sample of mice. The researchers first transplanted into the bone marrow a few hundred thousand MSCs that had been labeled with both iron-oxide (a molecule that essentially shades out the MRI signal) and a special protein that fluoresces when exposed to blue light. The team then operated on all of the mice, inducing a heart attack in one group. Over the following days, MRI scans showed a gradual darkening around the site of injury in the heart attack group, which was presumably due to the arrival of the labeled MSCs. The researchers validated this migration with fluorescent microscopy. The goal now is to devise a way to attach an MRI-sensitive marker to MSCs in humans who have suffered a heart attack. This would allow doctors to more closely study these cells, and perhaps devise treatments that can control their migration. Talk (TU-D-352-02), "Magnetic Resonance Imaging to Track Mesenchymal Stem Cells (MSCs) in a Murine Myocardial Infarction Model" is at 1:42 p.m. on Tuesday, July 29, 2008 in room 352. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9473-89709-126.pdf. 3) NEW IRRADIATION METHOD HOLDS POTENTIAL FOR IMPROVING BONE MARROW TRANSPLANT PRECONDITIONING STEP Preconditioning may one day be improved if a feasibility study by a group of Chicago-area researchers is validated in further studies. In experiments using a specialized manikin-like form that is the radiological equivalent of the human body, 98% of the intended structures received 99% of prescribed radiation dose, while normal body structures were spared from high doses. “Compared to conventional total body irradiation, this new approach reduced radiation to critical body parts such as the heart and the lungs by as much as 64% and 30% respectively which is a distinct improvement,” says lead researcher Bulent Aydogan, Ph.D. of the University of Chicago . Collaborators include researchers from the University of Illinois/Chicago and Loyola University Medical Center. The new technique is called linac-based Intensity Modulated Total Marrow Irradiation. “Linac” refers to the linear particle accelerator used to deliver precisely planned doses of radiation to the body. Rather than dosing the entire body equally, it selectively targets bone marrow locations and administers lower radiation doses to the rest of the body. Such accuracy is made possible by first mapping the patient’s body in 3D using a sophisticated computer scan. Next, computer programs optimize each beam of radiation into smaller “beamlets” so that each beam is individually suited to meet planned dosing goals for a given site. Finally, a linear particle accelerator (linac) delivers these planned doses to the patient. Radiation is therefore limited to bone marrow and cancerous structures, thus sparing critical organs in the body. If further evidence supports these early findings, the team hopes to move this new treatment to clinical trials involving humans. Talk (TU-D-AUD B-7), "Feasibility Study for Linac-Based Intensity Modulated Total Marrow Irradiation" will be at 2:24 p.m. on Tuesday July 29, 2008 in Auditorium B. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9119-58942-165.pdf. 4) ATTACKING TUMORS BIT BY BIT Common radiation therapy prescribes a uniform radiation dose to the entire tumor, even though it is commonly known that some regions resist radiation more than others. Researchers are therefore experimenting with ways to tailor the treatment, with so-called "dose painting," so that more radiation falls on the radio-resistant parts. For this to be effective, radio-resistance must be well-defined at the molecular level. This presumably can be done with PET scans using the radio-tracer FLT (fluoro-L-thymidine). When injected into the body, FLT is grabbed up by cells in the process of cell division. Therefore, rapidly-dividing cancer cells will look bright in a PET scan. Once treatment is started, those cells that remain bright would be considered radio-resistant, i.e. the radiation is not affecting their activity. But this simple brightness measure, called a standardized uptake value (SUV), is not the only way to locate non-responsive cells in a PET image. A more precise way (based on a parameter called KFLT) is to model how the radio-tracer travels through the body and is taken up by cells over time. Urban Simoncic of the Institut Jozef Stefan in Ljubljana, Slovenia, together with collaborators from University of Wisconsin-Madison compared the SUV and KFLT techniques on the exact same sets of PET scans and found that the two selected out different regions as being radio-resistant. This implies that a dose painting treatment based on one model would differ significantly from that based on the other. The researchers believe the community needs to address this discrepancy with more careful clinical investigation. Talk (MO-E-AUD C-1), "Dosimetric Differences for Dose Painting, Based On SUV Or KFLT FLT-PET Image Ratio" is at 4:00 p.m. on Monday July 28, 2008 in Auditorium C. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9061-97759-696.pdf. 5) NEW RADIATION THERAPY METHOD OFFERS SHORTER TREATMENT TIME In the IMRT method, a computer-controlled linear accelerator sweeps a narrow (1-2 cm wide) slit of radiation across the tumor from five to nine angles around the patient, one angle at a time. The VMAT method, in contrast, delivers radiation in a 360-degree arc while the beam aperture shape continuously changes. A variant of the VMAT technique, proposed by Pengpeng Zhang , an assistant attending physicist at the Memorial Sloan-Kettering Cancer Center, and his colleagues Laura Happersett and Gig Mageras, breaks the arc into 360 evenly divided beams. A computer program developed by the researchers adjusts the aperture shape and radiation dose of each beam to maximize the radiation to the tumor while keeping healthy tissue exposure down at acceptable levels. Because the resulting beam apertures are much larger in VMAT than in IMRT, treatment time is substantially less and patient exposure to radiation leakage from the accelerator is reduced. Zhang and his colleagues retrospectively evaluated the feasibility of this procedure in data from five patients treated for prostate cancer. The treatment times they calculated were reduced by up to 50 percent--from the 5 minutes typical for IMRT down to 2 ½ minutes-with a corresponding decrease in the amount of radiation leakage received by healthy tissues. Zhang hopes to extend the technique to the treatment of other cancers, including those of the head and neck, brain and pelvis. Talk (TU-D-AUD B-2), "Volumetric Modulated Arc Therapy: Implementation and Evaluation for Prostate Cancer Cases" will be at 1:42 p.m. on Tuesday July 29, 2008 in Auditorium B. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-8777-46582-702.pdf 6) TUNING X RAYS FOR THERAPY AND IMAGING The researchers use an instrument known as an electron beam ion trap (EBIT) to generate special X rays that can be tuned to a particular energy band so that they react in resonance with certain nanoparticles or contrast agents (for example, the contrasts used for diagnostic imaging) embedded into tumors. When the nanoparticles are struck by those resonant X rays, the particles absorb energy efficiently, then radiate this energy nearby, and thus achieve direct tumor cell damage. Some of the particles will fluoresce. These signature emissions "can be detected and differentiated almost like scanning for your favorite radio stations," says study head Yan Yu , Professor and Director of Medical Physics at Thomas Jefferson University, allowing very high-resolution imaging of the tumor, but with very low doses of radiation elsewhere. Although the technique has not yet been used on patients, "it will eventually allow us to use x-rays in a pristine, smart way," says Yu. Talk (TU-D-352-8), "Innovative Instrumentation for Resonant Cancer Theranostics" will be at 2:54 p.m. on Tuesday July 29, 2008 in Room 352. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9159-65642-404.pdf. 7) COMPUTER-AIDED ORGAN IDENTIFICATION Radiation therapy begins with a CT scan in which 100 or so individual images (slices) are combined to create a 3D map of the region around the tumor. During the following segmentation step, all the organs and sensitive tissues must be identified and outlined for each slice, so that the medical physicist can plan a treatment that provides the highest dose to the target, while sparing the surrounding healthy tissue. The resolution in CT scans is constantly increasing, which means more slices and more time required for segmentation. In addition, moving organs like the lung are starting to be scanned several times to form a time sequence. This can multiply by 10 the number of images an expert must analyze. To help with this overwhelming load, Yu-chi Hu and Gig Mageras of the Memorial Sloan-Kettering Cancer Center in New York, NY, along with Michael Grossberg of the City College of New York have developed a computer program that can segment organs with just a small amount of user input. Starting with one CT image, the user makes a crude outline of each organ. The computer takes this rough sketch and plugs it into a statistically-based algorithm, which it then uses to generate contours in subsequent images. The user checks the computer-drawn boundaries and can correct mistakes with tiny brushstrokes on the computer screen. These corrections are reincorporated by the software to better refine the algorithm. With funding from the NIH, the team tested the user interface on several CT scans and found that on average an image could be segmented in roughly 6 seconds with the computer's help, instead of the 30 seconds or more in the unaided case. The researcher's algorithm correctly identified 98% of the image pixels, which was a higher precision than other contour-drawing algorithms that the researchers tested. The group is now planning to put the system into clinical use within 6 to 9 months. Talk (TH-D-332-2), "Semi-Automatic Medical Image Segmentation with Adaptive Local Statistics in Conditional Random Field Framework" is at 1:42 p.m. on Thursday July 31, 2008 in Room 332. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9074-9005-850.pdf. 8) NEW TECHNIQUE TO ESTIMATE LUNG TUMOR CHANGES Issam M. El Naqa , an assistant professor of radiation oncology at Washington University in St. Louis, and his colleagues have devised a novel solution. Their semi-automated system combines two types of computer algorithms previously only used separately to process data from computerized tomography (CT) scans of the lungs. So-called deformable regression algorithms are used to create a consistent set of coordinates on which tumor position and size can be mapped over the course of treatment, and segmentation algorithms allow tumors to be precisely located and distinguished from other lung tissue (or "segmented") in CT images. El Naqa and his colleagues, realizing that "both approaches could significantly benefit from the results of the other algorithm if coupled in the same framework," created a new program that does just that. Talk (WE-E-AUD C-07), "A Robust Approach for Estimating Tumor Volume Change During Radiotherapy of Lung Cancer" is at 5:12 p.m. on Wednesday July 30, 2008 in Auditorium C. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9234-11920-790.pdf. In related work, researchers at the University of California, San Diego, have developed a computer algorithm to localize the position of lung tumors during fluoroscopic imaging. Fluoroscopic imaging permits clinicians to view images obtained in real time, but because of the poor contrast between lung tumors and normal lung tissue, tumors can be essentially invisible. However, the tumors may move in concert with anatomic features that are easier to visualize and that can serve as stand-ins. "The algorithm that we are developing will be able to automatically select surrogate anatomic features whose motions are correlated with tumor motion," says study senior author Steve Jiang , Associate Professor and Director of Research in the Department of Radiation Oncology at UCSD. "Thus, by tracking their motion we can derive the positions of the unseen tumors." Talk (TU-C-351-09), "Fluoroscopic Lung Tumor Tracking" is at 11:36 a.m. on Tuesday July 29, 2008 in Room 351. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-8851-2876-103.pdf. 9) HOSPITAL COMPILES EXPERIENCE WITH LATEST IMAGE-GUIDED RADIATION THERAPY In 2003, the TomoTherapy® Hi•Art® treatment system became one of the first to combine intensity modulated radiation therapy with CT scanning to ensure that the patient is well-positioned to receive the highly-sculpted beam energy. One of the specifications that makes the TomoTherapy hardware unique is that radiation is applied by a constantly rotating beam through which the patient advances on a slow-moving couch. The result is a helically-shaped radiation delivery. Even though the TomoTherapy system is more automated than traditional treatment plans, the user must choose parameters such as beam size, delivery modulation, gantry rotation speed, and how fast the couch moves. As the technology is still fairly new, not many medical physicists are very familiar yet with what values to use. Dr. Movahed and colleagues have compiled a list of best-fit parameters that draw from their own trial and error with the TomoTherapy machines. The procedures covered include prostate, lungs, brain, liver, head & neck, breast, pelvis and pancreas. Talk (WE-C-AUD C-05), " Analysis of Best Fitting Tomo Treatment Planning Parameters for Prostate, Lung, Breast, Brain, Liver, Head & Neck, Breast, Pelvis and Pancreas Lesions From Our 3 Years Experience Planning for Nearly 1000 Patients" is at 10:48 a.m. on Wednesday July 30, 2008 in Auditorium C. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9657-68328-620.pdf 10) CELEBRATING 50 YEARS OF WOMEN IN MEDICAL PHYSICS In 1958 when the organization was formed, 20 of its 133 members -- 15% -- were women. In 2008, women make up 19% of the AAPM membership (1,297 women and 6,597 men. “This ratio is much lower than in other countries. For example in the United Kingdom, approximately 50% of undergraduates pursuing medical physics are women,” says Cari Borrás, D.Sc., Women’s Coordinator of the Minority Recruitment Subcommittee of the AAPM. (cariborras@starpower.net) “This discrepancy between the U.S. and Europe suggests there's a great role for AAPM to play in women's medical physics education to open this important career field to more women.” From early pioneering work to current discoveries, AAPM's female members have made seminal contributions in radiology, nuclear medicine and radiation therapy, as well as in some non-traditional areas of medical physics such as mechanics, optics and electromagnetism. They have also held key leadership roles within the organization of the AAPM, and won distinguished awards. These awards include the Nobel Prize in Physiology or Medicine in 1977, by Rosalyn A. Yalow; the AAPM William D. Coolidge Award in 1977 by Edith E. Quimby, and the AAMP Award for Achievement in Medical Physics by Mary Louise Meurk in 2000, Azam Niroomand-Rad in 2006, and Marilyn Stovall in 2007. Symposium (WE-E-342-2), "(Part II) 50 Years of Women in Medical Physics -- Symposium organized by the AAPM Minority Recruitment Subcommittee" is at 4:00 p.m. on Wednesday July 30, 2008 in Room 342. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9986-65686-861.pdf. 11) PREVENTING MEDICAL ERRORS IN RADIATION THERAPY Like all hospital disciplines, the field of medical physics has a responsibility to try to eliminate preventable medical errors. The AAPM has a working group on preventing errors in radiation oncology, and since the turn of the century has worked to enhance the safety and quality of patient care. One of the issues that has emerged in the last few years is the increasing need to develop more and more sophisticated safety and quality assurance measures to adequately handle the complexities of advancing technology. As new and sophisticated technology has improved the ability to deliver radiation more accurately, conforming doses to the tumors being treated for instance, it has also increased the complexity of the instruments and procedures. With increasing complexity come more opportunities for errors, and so new medical physics technologies have also created the need for new safety measures that are equally sophisticated. Peter Dunscombe , who is Director of Medical Physics at Tom Baker Cancer Centre in Calgary, Canada, is leading a symposium that will present an overview of the latest sophisticated safety methods used to ensure quality of care for people undergoing radiation therapy. He and his co-participants will also examine how audits of safety and quality assurance programs might be conducted. They will discuss a European database that allows information on medical errors to be shared internationally, and they will examine errors from the point of view of the Nuclear Regulatory Commission. Symposium WE-C-350-1, "Quality in Radiation Therapy: what is it and how do you achieve it?" is at 10:00 a.m. on Wednesday July 30, 2008 in Room: 350. **************************************************************** HOW TO COVER THE MEETING Reporters who would like to cover the conference remotely will find releases and articles on the Virtual Press Room highlighting many of the interesting and important talks presented at the meeting. Even if you can't make it to Houston, the Virtual Press Room will make it possible to write stories about the meeting from your desk. ABOUT AAPM
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