The 52nd meeting of the American Association of Physicists in Medicine (AAPM) convenes from July 18 - 22, 2010 in Philadelphia, PA.
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.
Highlights of the meeting are listed below.
- Nanocoated Gold Bullets Help Destroy Tumors, Improve Radiation Therapy
- Tumor Tracking with Smart Probing – A Stock Market Approach
- Six-Year Study Finds Few Permanent Side Effects After SBRT for Lung Cancer
- A Library of Lung Tumors
- Tactile Tumor-Imaging Device
- Making Tumors Glow Could Reveal Their Hiding Spots
- IMRT Safe and Effective for Treating Cancers of Paranasal Sinus
- New Nanotechnology Capsule Delivers Cancer Drug, Then Heat
- New Multisource X-Ray Imaging Technology
- Testing Proton Clusters
- Solid-State X-Ray Intensifiers
- To Treat Cancer, Subdivide and Conquer
- Red-Flagging Cancer
- More Meeting Information
1) NANOCOATED GOLD BULLETS HELP DESTROY TUMORS, IMPROVE RADIATION THERAPY
Image-guided radiation therapy targets tumors in organs that tend to move during treatment, such as the prostate gland or the lungs, as well as tumors near vital organs. Often, inert markers are implanted into the body to help radiation oncologists pinpoint the cancerous tissue.
A group of researchers wants to draft these markers to deliver drugs that will combat cancer and make the tumor more sensitive to radiation. The drugs can be tailored to different tumor types, the researchers say.
"Right now, these markers are just passive implants that are inserted into the tumor," says Srinivas Sridhar, a physics professor at Northeastern University and director of the university's Electronic Materials Research Institute. "We're making them active and smart using nanotechnology," he said.
The challenge is designing a system that will work over an extended period of time and target the entire tumor without affecting healthy tissue. The team has already developed a nanoscale polymer coating containing anti-cancer drugs for gold fiducials, which are commonly used markers.
Now, the researchers report they can precisely tailor drug dosage and rate of release in laboratory tests lasting up to three months. The nanoporous morphology of the polymer coatings enabled the controlled release of molecules and nanoparticles. The results also help refine the team's models of drug release kinetics.
The group includes collaborators Mike Makrigiorgos and Robert Cormack from Brigham & Women's Hospital and Dana-Farber Cancer Institute.
The Presentation "Release Kinetics of Radio-Sensitizers From Nanoporous Coatings On Gold Fiducials: Biological In-Situ Dose-Painting for IGRT" by C Stambaugh et al. will be at 4:12 p.m. on Wednesday, July 21 in room 204B of the Pennsylvania Convention Center.
2) TUMOR TRACKING WITH SMART PROBING – A STOCK MARKET APPROACH
Pinpointing tumor location and behavior can be as risky and frustrating as estimating the rise and fall of stocks in the market. A new model, developed by Dan Ruan, Ph.D., an instructor in radiation oncology at Stanford University, and colleagues, employs tactics similar to those used by market analysts. Ruan will present the model at the 2010 annual meeting of the American Association of Physicists in Medicine, July 18-22, in Philadelphia, PA.
"In estimating the stock market," she says, "people try to predict how stock will behave based on historical data and the company's portfolio." The mathematical model uses data on how tumor motion has changed during a course of radiation treatment in addition to real-time images of a tumor to calculate how much confidence the physcists can have about an instantaneous tumor position estimate. The goal of the work is to reduce the number of times intrafraction X-ray needs to be triggered as tumor localization measurement, thereby reducing the total amount of radiation a patient receives.
With a typical image-guided radiotherapy (IGRT) protocol, X-rays are used at a fixed frequency to validate the location of the tumor target. This rate may be increased to improve the localization accuracy. Ruan's model, however, which she calls adaptive, aims to accurately localize tumors in real-time by imaging smarter, rather than more frequently. It makes online decisions as to whether or not it is necessary to take a new X-ray image during treatment. In test cases that she will present, imaging frequency was reduced by 40 to 50 per cent without sacrificing tumor localization accuracy, meaning that the X-ray dosage to the patient was essentially halved or close to halved.
Reducing imaging radiation is an important goal for oncologists because radiation is associated with secondary malignancies, especially in pediatric patients who typically live for a long time after surviving their cancer. The model should be helpful in these cases, and particularly for tumors that because of their location – lung, thorax, and abdomen – are difficult to locate because of the body movement that occurs as patients breathe.
The Presentation " Reducing Imaging Dose Without Sacrificing Target Localization Accuracy: A Feasibility Study Byline D Ruan" by D Ruan and P Keall will be at 10:24 a.m. on Tuesday, July 20 in room 204B of the Pennsylvania Convention Center.
This research was supported by the National Cancer Institute and the AAPM Seed Funding Initiative.
3) SIX-YEAR STUDY FINDS FEW PERMANENT SIDE EFFECTS AFTER SBRT FOR LUNG CANCER
A six-year study of lung cancer patients treated with stereotactic body radiation therapy (SBRT) found few people experienced significant lasting side effects from the relatively new technique.
SBRT hits tumors with extremely high (but narrowly focused) radiation doses, typically given in three to five treatments. The researchers evaluated lung density changes in 63 people who received SBRT between 2003 and 2009. After six months, patients had transient density increases of up to 100 percent compared to their pre-treatment lung density. After 12 months, the density changes stabilized to less than 50 percent of pre-treatment levels, and lung morphology was mostly unaffected.
"We saw some changes, but nothing of a catastrophic nature or anything that implies we're going in the wrong direction with this treatment," says co-author Brian Kavanagh, a professor of radiation oncology at the University of Colorado Denver School of Medicine. "The first impression is very much a reassuring one."
Understanding how normal lung tissue is affected by the intense radiation will help physicians avoid excess injury to healthy tissue and more aggressively treat tumors, says Kavanagh.
The researchers also discovered that some patients had subtle changes in normal tissue that appeared to signal later development of side effects such as inflammation.
"These early signals will give us an opportunity to anticipate potential problems and personalize treatments," says co-author Moyed Miften, a professor of radiation oncology at UC Denver.
Funding sources: University of Colorado Denver Cancer Center
The Presentation "Temporal Dose-Response of Normal Lung Tissue in Patients Treated with Stereotactic Body Radiation Therapy for Lung Tumors" by B Kavanah et al. will be at 1:30 p.m. on Monday, July 19 in room 204B of the Pennsylvania Convention Center.
4) A LIBRARY OF LUNG TUMORS – THE LUNG IMAGE DATABASE CONSORTIUM AND IMAGE DATABASE RESOURCE INITIATIVE
A database of more than one thousand lung scans, the culmination of a nine-year effort on the part of seven academic institutions and eight medical imaging companies, has been completed and is now available to medical imaging investigators. The project will be presented by Samuel G. Armato III, Ph.D., associate professor of radiology at the University of Chicago, during the 2010 annual meeting of the American Association of Physicists in Medicine, July 18-22, in Philadelphia, PA.
The rationale for the project, according to Armato, was to assist developers of automated detection systems, often referred to as CAD (computer-aided diagnosis) by offering them a "standard of truth" against which to compare their methods. All of the images contained in the database are clinical CT scans (computed tomography) that were read manually by a team of four thoracic radiologists, working in two phases. In the first phase, each radiologist worked independently of the others; in the second phase, they reviewed one another's findings in order to achieve a more complete read of each scan.
The database contains 1018 CT scans and a total of 7371 identified lung nodules, as well as the radiologists' markings of the larger nodules' outlines and characteristics, including subtlety, spiculation, solidity and margin. The database contains both larger (greater than three millimeters) and smaller nodules. "There is a lot of discussion in the clinical community about the significance of small nodules," Armato said. The radiologists marked the smaller nodules to indicate their presence but provided more extensive information about the larger nodules.
The Lung Image Database Consortium (LIDC) was initiated by the National Cancer Institute in 2001 with the participation of five academic centers and expanded in 2004 by the Foundation for the National Institutes of Health to create the Image Database Resource Initiative (IDRI). "There was a huge commitment on the part of the NCI," said Armato, pointing out the "extent of academic and intellectual effort" marshaled toward the completion of the project.
The web site through which the database may be accessed is http://ncia.nci.nih.gov.
The presentation "The Lung Image Database Consortium (LIDC) and Image Database Resource Initiative (IDRI): A Completed Public Database of CT Scans for Lung Nodule Analysis" by S Armato et al. will be at 8:30 a.m. on Wednesday, July 21 in room 201B of the Philadelphia Convention Center.
5) TACTILE TUMOR-IMAGING DEVICE
Chang Hee Won and his colleagues at Temple University have made a novel tactile tumor-imaging device by exploiting the optical properties of waveguides -- which are planar, flexible and transparent probes.
Light traveling in a transparent waveguide will normally not leak out because of the principle of total internal reflection; if the refractive index of the guide is more than that of the surrounding material, a light ray approaching the wall of the guide will be reflected back into the guide. If, however, the guide becomes deformed because an object compresses the waveguide, then light can escape at that point. An imager will capture the light and from this image the mechanical properties of the objects may be determined.
In this case, the object in question is a tumor. In the case of the Temple research the waveguide consists of a flexible probe fed with light from a light emitting diode (LED). Light exiting the probe is caught on a camera, and from the emergent light the scientists are able to measure tumor diameters to within about 4 percent and tumor depths to 7.6 percent.
"We have performed a phantom study and [imaged] globus tumors in mice," says Won. "More sophisticated machines such as MRI will measure the size and depth more accurately, but the elasticity information is unavailable with MRI. Conversely, methods such as sonoelastography will provide the elasticity information, but this is a much more complex machine. Our device provides a means of detecting size, depth, and elasticity information in a relative simple device."
The next step, Won says, is to move from imaging mouse to human tumors with the device. This he is now doing with collaborators at the Thomas Jefferson University Hospital and Cooper University Hospital.
Small-scale human tests will be carried out within this year. Won says that this device has a potential to be used in breast cancer screening if it proves successful.
A website with more information: http://www.temple.edu/csnap
The presentation "Design and Evaluation of an Optical Tactile Imaging Device for Tumor Detection" by C Won et al. will be at 3:00 p.m. on Sunday, July 18 in the exhibit hall of the Philadelphia Convention Center.
6) MAKING TUMORS GLOW COULD REVEAL THEIR HIDING SPOTS
Getting a clear picture of a hidden tumor remains a major hurdle in cancer treatment. Researchers from the Stanford University School of Medicine hope to solve this problem with a molecular imaging system that uses X-rays to make tumor cells shine brightly.
The hybrid X-ray/optical imaging system relies on nanosize phosphors – imaging markers that convert X-ray energy to light. The markers are made of gadolinium oxysulfide and coated with either terbium (glows green) or europium (glows red).
In laboratory tests, the hybrid system showed a 260 percent contrast difference between simulated normal and cancerous tissue, the researchers report. A standard X-ray showed a 0.6 percent contrast difference.
The team also found that very low concentrations of the nano-phosphors produce high contrast pictures. "We have determined that the minimum detectable concentration is far lower than conventional contrast enhanced X-ray imaging, for the same dose, meaning that tumors may be detected at the earliest, most treatable stage," says lead author Colin Carpenter, a Stanford postdoctoral fellow.
The system could aid both drug discovery and disease treatment. For example, attaching the phosphors to certain biomarkers would help researchers better visualize the distribution and efficacy of new anti-cancer drugs, says Carpenter.
"However, in my mind, the most exciting application for this system is a device to aid surgeons in the complete excision of diseased tissue," he adds. "Currently, it is very difficult to remove all the tumor cells in the tissue, because surgeons don't have a tool that is sensitive enough. Allowing a real-time visualization of these tumor cells could significantly improve treatment."
The presentation "Development of an X-ray/Optical Luminscence Imager for Improved X-ray Contrast Sensitivity" by CM Carpenter et al. will be at 4:00 p.m. on Wednesday, July 21 in 204B of the Philadelphia Convention Center.
This research was supported by the NIH In vivo Cellular and Molecular Imaging Center at Stanford, the NSF and the DoD.
7) IMRT SAFE AND EFFECTIVE FOR TREATING CANCERS OF PARANASAL SINUS
Intensity-modulated radiation therapy (IMRT) appears to be a safe and effective treatment for cancers in the nose area, known as paranasal sinus cancers, new data suggest. This is a boon to patients suffering from a cancer that is difficult to treat due to its closeness to the optic nerve and the interactions of air and tissue that can disrupt precision delivery of radiation. Both hold potential for causing blindness.
But clinical outcomes are encouraging from a new collaborative study of 31 patients treated with IMRT at Fox Chase Cancer Center in Philadelphia. Notes Fox Chase lead researcher Aruna Turaka, M.D.: "Our results show there were no loss of vision or vision disturbances such as floaters, and preserving vision is always the main concern."
Researchers found no high grade complications to either vision or salivary function. With a median follow up of 27 months the 2- and 5-year overall survival rates were as high as 89%, for early stages, and declined with time to 66% at 5 years. A few patients had recurrent or residual cancer, but overall, Dr. Turaka says, "IMRT appears be a promising and well-tolerated treatment method."
The presentation "Intensity-Modulated Radiation Therapy (IMRT) for the Para-Nasal Sinus (PNS) Malignancies: Outcomes From Fox Chase Cancer Center (FCCC)" will be at 3:00 p.m. on Sunday, July 18 in the exhibit hall of the Philadelphia Convention Center.
8) NEW NANOTECHNOLOGY CAPSULE DELIVERS CANCER DRUG, THEN HEAT
Nanoparticles are tiny bits of metal and other materials that spark a lot of enthusiasm in the cancer research world because the particles can be precisely targeted to a tumor and therefore need lower doses to be effective. This translates into fewer side effects for patients.
Now there's more. Researchers at Baylor College of Medicine in Houston, Texas have developed a targeted nanocapsule system that delivers two cancer therapies simultaneously: the chemotherapy agent doxorubicin and heat therapy (hyperthermia).
"The great thing about our magnetic, nanoparticle-assembled capsule," explains lead researcher John McGary, "is that it's a multifunctional device that can be used simultaneously to release the desired drug concentration at the tumor site while heating up the tumor cells."
The system is based on nanoparticle-assembled capsules (NACs), structures that form themselves as a result of their chemical properties. The capsules contain the chemotherapy agent doxorubicin. An external magnetic field passed over the nanocapsule releases doxorubicin and also heats up the NAC solution, heating the tumor cells to more than 50° C to kill them.
NACs have been tested in the lab to study the release and heating rates. Future studies will test cell culture and animal studies, Dr. McGary says.
The presentation "Nanoparticle Assembled Capsules for Target Drug Delivery, Controlled Release and Hyperthermia" by J McGary et al. will be at 3:00 p.m. on Sunday, July 18 in the exhibit hall of the Philadelphia Convention Center.
This research was supported by the Mike Hogg fund and Golfers Against Cancer.
9) NEW MULTISOURCE X-RAY IMAGING TECHNOLOGY
Rather than use a single source of X-rays to image patients, scientists at GE Global Research have developed a way to use an array of separate sources, each of which covers a small portion of the patient. Each can be modulated in intensity so as to achieve sharp images with the lowest possible amount of radiation. Only one source is active at a time, and can be modulated so that within one position the desired intensity delivers a shaped dose. It's like a personalized CT scanner for each patient.
The GE sources achieve beam powers of 60 kW. Images are sharper than usual because the conical X-ray beams are narrower than for traditional CT machines and produce less scattered X-rays. This eliminates the need for baffles to block scattered X-rays (which would otherwise degrade the image quality), allowing still more detector cells to be brought into play. The detector in the inverse geometry CT system (IGCT) is about one-fifth the size used in conventional CT units. A higher active area also means the possibility of realizing smaller cells and higher spatial resolution.
According to GE scientist Kris Frutschy, multisource technology is at the research stage and is not yet commercially available. Furthermore, the reconstruction software will necessarily be more sophisticated for multisource systems since the data from all sources must be calibrated and combined.
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.
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.
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.
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.
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.
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.
- Main Meeting Web site: http://www.aapm.org/meetings/2010AM
- Meeting program:
- AAPM home page: http://www.aapm.org
SOURCE American Association of Physicists in Medicine