4D proton therapy, radiation-resistant tumors, interpreting medical images

06/28/05

Medical physics meeting features innovations coming to a hospital near you

College Park, MD, June 28, 2005 - How can the act of simply imaging a tumor reveal cancer regions that will be invulnerable to normal levels of radiation? What are the biggest errors in reading image scans and how can they be fixed? What recent advances are making subatomic protons increasingly desirable for treating lung tumors? What can local governments do to better prepare for radiological emergencies?

These and other questions will be addressed at the 47th Annual Meeting of the American Association of Physicists in Medicine (AAPM), which will take place July 24-28, 2005 in Seattle, WA at the newly expanded Washington State Convention & Trade Center, located at Pike Street and 7th Avenue. The scientific program will begin on Sunday, July 24 at 8:00 AM and conclude on Thursday, July 28 at noon. Approximately 1152 papers will be presented on subjects at the intersection of physics and medicine. Many of these topics deal with the development of state-of-the-art imaging and therapeutic devices, and the new techniques that go along with them.

CONTENTS

This news release begins by containing information on how to cover the meeting, then describes the President's Symposium on the World Year of Physics as well as some public-policy sessions, and concludes by highlighting six scientific papers/sessions at the meeting.

HOW TO COVER THE MEETING

The AAPM meeting webpage (http://www.aapm.org/meetings/05AM/) contains links to the full program. Starting in early July, a Virtual Pressroom will contain additional meeting tips, lay-language papers, and press releases. Reporters who would like to attend the meeting should fill out the press registration form (http://www.aapm.org/meetings/05AM/documents/pressreg.PDF) by July 15. Even if you can't make it to Seattle, the Virtual Pressroom and this news release are designed to make it possible to cover meeting highlights from your desk. For assistance in contacting researchers and setting up interviews, please do not hesitate to contact the science writers listed at the top of the news release.

PRESS LUNCHEON

A press luncheon featuring some of the most newsworthy topics at the meeting will be held in room 401 between 12:00-1:30 PM on Tuesday, July 26. Topics will include 4D proton therapy, lighting up radiation-resistant cancer regions, first clinical trials of a mammography alternative, and image-guided radiation therapy (IGRT), in which onboard imaging equipment guides radiation more precisely than previously possible during a cancer therapy procedure. Further details will be given in an upcoming news release. RSVP Ben Stein at bstein@aip.org by July 15 if possible.

PRESIDENT'S SYMPOSIUM FEATURES EINSTEIN AND THE WORLD YEAR OF PHYSICS

The AAPM President's Symposium, moderated by AAPM President Howard Amols, which focuses on the World Year of Physics that has been declared for 2005 (http://www.wyp2005.org/). John Rigden (jrigden@aip.org), a physicist, historian, and popular science writer, will discuss how in a period of six months, one week, and two days, in 1905, Einstein wrote five papers that helped form the bedrock of modern physics. Medical physicist Peter Almond (palmond@mdanderson.org) will talk about the concurrent early history of radiation physics, and how news of Wilhelm Roentgen's 1895 discovery spread like wildfire and led quickly to medical uses of x rays.

TERRORISM RESPONSE, MEDICAL ERRORS, INSURANCE REIMBURSEMENT

A weeklong series of professional symposia will cover various public policy issues that affect the general public. On Wednesday, July 27, at 10:00 AM, Janice Adair, the Assistant Secretary of Washington State's Division of Environmental Health, will describe emergency preparedness and terrorism response training for professionals at the statewide level. On Thursday, July 28, at 10:00 AM, Debra McBaugh, the chairperson of the Conference of Radiation Control Program Directors, will discuss how medical physicists have unique skills that can assist states in terrorism response. McBaugh was part of the State of Washington's team that participated in a national exercise that included responding to a simulated dirty bomb attack. Other sessions throughout the week cover topics such as how Medicare and Medicaid reform are affecting insurance reimbursement of radiological procedures, medical errors, the impact of recent Nuclear Regulatory Commission training and experience regulations on the handlers of radioactive material in diagnosis and therapy, and reforms in the radiological health programs at the FDA.

HIGHLIGHTS OF THE SCIENTIFIC PROGRAM

The following is a sampling of some of the many noteworthy talks that medical physicists will present at the meeting.

I. PROMISING FIRST IMAGES FROM HUMAN CLINICAL TRIALS OF MAMMOGRAPHY ALTERNATIVE
II. LIGHTING UP RADIATION-RESISTANT TUMOR REGIONS
III. READING BETWEEN THE LINES OF MEDICAL-IMAGE INTERPRETATION
IV. TREATING LUNG CANCER WITH 4D PROTONS
V. HYBRID MACHINE PERFORMS MRI AND RADIATION THERAPY
VI. ELECTRON TECHNIQUE IMAGES CRUCIAL OXYGEN LEVELS

I. PROMISING FIRST IMAGES FROM HUMAN CLINICAL TRIALS OF MAMMOGRAPHY ALTERNATIVE

Researchers will present some of the first images from human clinical trials of breast CT imaging, a potential improvement over traditional mammography that aims to catch breast cancer earlier while eliminating patient discomfort. Traditional mammograms involve squeezing the breast between two plates and firing an x-ray that images the breast all at once. In breast CT, the patient lies down on a table and places one breast at a time through a circular opening, while a CT scanner produces 300 images per breast, in a period of just 17 seconds, to build up 3D images.

According to the inventors of the new approach, including John Boone of the University of California at Davis (jmboone@ucdavis.edu), the technique has the potential to catch tumors that are the size of a pea, as opposed to the garbanzo-sized tumors that can be caught with standard mammography, while not requiring painful breast compression. In addition, the 3D images can catch buried tumors that are ordinarily obscured by 2D mammograms.

At the AAPM meeting, Thomas Nelson of the University of California at San Diego (tnelson@ucsd.edu) will present some of the first images from the clinical trials. Nelson and his colleagues report that the breast CT images show impressive detail of the unique tissue structure of the breast and high-contrast glandular detail. If the first clinical trial successfully demonstrates that breast CT can detect tumors as well as mammograms, a larger-scale clinical trial, which can occur in as early as 2 or 3 years, will test if the technique can detect tumors earlier than mammograms. Breast CT will expose the patient to about as much radiation as a standard mammography. (Paper SU-EE-A2-3, Sunday, 2:15 PM; for more information, see http://www.ucdmc.ucdavis.edu/newsroom/releases/archives/cancer/2005/breast_ct5-2005.html).

Meanwhile, researchers at the University of Rochester, the University of Massachusetts, and Duke University are also independently pursuing breast CT machines as an alternative to standard mammography.

II. LIGHTING UP RADIATION-RESISTANT TUMOR REGIONS

Andrei Pugachev of Memorial Sloan-Kettering Cancer Center in New York (pugachea@mskcc.org) will present progress towards reliably finding and imaging regions of a tumor that are not destroyed by ordinary levels of radiation.

Like an overdeveloped mall built suddenly in a small town, aggressive tumors overwhelm their surroundings; they often grow faster than the blood vessels supplying oxygen to them. Such fast-growing tumors often contain "hypoxic regions," or areas of lower-than-normal levels of oxygen. As it turns out, these hypoxic tumor regions are resistant to radiation. That's because when radiation damages DNA in a tumor cell, oxygen is needed to carry out additional chemical reactions to make the damage permanent.

Currently, there are radioactive tracers that, when injected into the blood supply, will tend to bind to hypoxic regions in tissue and light them up for doctors to see in a PET scan. Unfortunately, however, some tracers behave very differently in different tumors, and their accuracy in mapping hypoxic regions is not known.

Pugachev and colleagues have devised a technique for verifying that PET tracers work as intended. They compare how a PET tracer distributes itself in a tumor to the distribution of a proven marker of hypoxia, such as the chemical pimonidazole. In animal studies of prostate tumors, they found that two specific PET tracers were reliable and one was not.

By validating PET tracers in a two-step process (first, using animal tumor models and then patient tumor biopsies), researchers hope that they will soon be able to produce reliable, in-vivo images of hypoxic tumor regions (Paper MO-D-I-609-8, Monday, 1:30 PM).

III. READING BETWEEN THE LINES OF MEDICAL-IMAGE INTERPRETATION

Properly interpreting a medical image can involve a life-or-death decision about the course of a patient's treatment. In recent years, computers have helped image perception in two ways. First, algorithms can be used to process digital information to make images clearer, such as by enhancing contrast. Second, algorithms can aid in detecting and possibly classifying lesions.

But there are still plenty of chances for errors in interpretation. Sometimes a radiologist will make a mistake; they might miss lesions (false negatives) or report something as positive when in fact there is nothing there (false positives).

Elizabeth Krupinski (krupinski@radiology.arizona.edu, http://www.radiology.arizona.edu/krupinski/index.html), who holds joint appointments in the radiology and psychology departments at the University of Arizona, is a leader in Medical Image Perception research, which seeks to discover the root causes of interpretation errors and find ways to avoid them. She is the first of several speakers on this topic at session WE-E-I-609 (Wednesday, 3:30-5:00 PM), which is designed to highlight the importance of medical image perception research to a community of researchers that may not be that familiar with the topic or know why it is important.

As Krupinski points out, the radiologist is the final link in the imaging chain. He or she holds the final responsibility for interpreting the image data and making a diagnostic decision that will affect patient care. Hence there is a need for examining how the radiologist views images and what factors influence the interpretation process.

IV. TREATING LUNG CANCER WITH 4D PROTONS

Compared to the x rays traditionally used in radiation therapy, protons offer the ability to destroy lung tumors just as competently while inflicting less damage to surrounding healthy tissue.

In a small experimental patient study, researchers have increased the effectiveness of using protons to treat lung tumors. In traditional radiation therapy, one must use multiple beams of x-rays to deliver a uniform dose to a lung tumor; often at least one of the x-ray beams will exit from the healthy (non-tumor-containing) lung and potentially damage it. On the other hand, positively charged, subatomic protons only travel a limited distance through the body; they never make it to the other lung, and they also are more likely to spare nearby organs such as the esophagus and heart.

In any radiation treatment of the lung, it is a challenge to keep the radiation on target while the tumor moves as a result of patient breathing. In the 4D approach, one takes into account how the patient's breathing moves the lung back and forth over time (the fourth dimension) so that the radiation hits the tumor precisely over all phases of a patient's breathing cycle.

Now, researchers at Massachusetts General Hospital have applied the 4D approach to proton therapy. In a study of four patients, they have found that planning and carrying out 4D proton therapy delivers excellent dose levels to lung tumors in all cases.

The only thing preventing this technique from wider use is the need to develop an algorithm that cuts down the currently lengthy time it takes to calculate and plan the proton beam's direction and intensity for each breathing phase. The 4D approach is also applicable to radiation therapy using carbon ions, which is currently being used to help defeat lung cancer in a couple of centers in Japan. (Paper WE-E-J-6C-7, Wednesday, 3:30 PM; contact Martijn Engelsman, now at MAASTRO clinic, Netherlands, martijn.engelsman@maastro.nl)

V. HYBRID MACHINE PERFORMS MRI AND RADIATION THERAPY

Combining MRI imaging and cancer radiation therapy in a single procedure addresses the problem of maintaining accurate positioning while performing radiotherapy over a period of several days or more. A procedure developed by a collaboration of scientists at University Medical Center Utrecht (Netherlands), Philips Research Hamburg (Germany), and Elekta Oncology Systems (Great Britain) uses a slightly modified commercial MRI unit surrounded by a movable accelerator (producing 6-megavolt beams of electrons to generate x rays). The whole process of tumor imaging and dose delivery is under computer control.

According to Jan Lagendijk (J.J.W.Lagendijk@radth.med.uu.nl, www.radiotherapie.nl), he and his colleagues expect that this new design will become the next-generation radiotherapy treatment machine. The superior image quality of the MRI available on line during treatment should have a large impact on the design of individualized radiation-therapy treatment plans. (MO-E-J-6B-3, Monday, 4 PM; for another recent hybrid machine that combines MRI and x-ray methods, see a June 2005 Physics Today article at http://www.physicstoday.org/vol-58/iss-6/p22.html).

VI. ELECTRON TECHNIQUE IMAGES CRUCIAL OXYGEN LEVELS

Taking advantage of the properties of electrons in certain biochemical compounds, Charles Pelizzari (c-pelizzari@uchicago.edu) and his colleagues use a novel technique to form images of the oxygen distribution of small animals with millimeter spatial resolution.

Developing these tools at the Center for In-Vivo EPR Imaging directed by Howard Halpern at the University of Chicago, the researchers create these important maps of oxygen levels by magnetically manipulating the unpaired electrons in certain oxygen-containing molecules such as free radicals. Most electrons in atoms and molecules form pairs that mutually cancel out their internal magnetic properties, but unpaired electrons can give the atom/molecule "paramagnetic" properties that cause them to be weakly attracted to an external magnetic field.

Electron paramagnetic imaging (EPRI) obtains pictures of molecules with unpaired electrons in a similar way that MRI obtains images of atomic nuclei such as the hydrogen in water: an image is formed when paramagnetic molecules, lined up in a magnetic field, absorb and then re-emit electromagnetic waves in or near the microwave portion of the spectrum. Using a series of magnetic fields that vary in strength over a given region of space, these emissions can be reconstructed into a 3D image.

Where EPRI is advantageous over MRI is in providing quantitative images of the distribution of oxygen in living tissues. Oxygen, or its absence, is central to many diseases; it is a factor in cancer aggressiveness and in the response to radiation and chemotherapy. Pelizzari expects that one day this EPR methodology will obtain submillimeter-resolution maps and also be scaled up to human dimensions. A potential long-term benefit of EPR imaging should be in providing quick feedback on the results of cancer therapy in days or even hours, without the use of radioactivity. In their talk at the meeting, Pelizzari's group will present EPR oxygen images superimposed on MRI anatomical images (WE-D-I-609-8)

Source: Eurekalert & others

Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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