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Contact: Jason Bardi
jbardi@aip.org
301-209-3091
American Institute of Physics

Cancer research highlights

July 24, 2008 -- HALF OF ALL AMERICANS will be diagnosed at some point in their lives with cancer, the number two killer in the United States. One of the professions at the frontlines in the battle against cancer are medical physicists -- scientists who use the power and innovation of physics to study and solve the most pressing medical problems.

Medical physicists help to develop new imaging technologies, such as dedicated breast CT scans, and improve existing ones. They devise new therapeutic techniques, including new radiotherapy applicators for cervical cancer treatment and procedures to focus radiation using nanoparticles, quantum dots, and other discoveries from the cutting edge of science, and they create methods to assess the safety and effectiveness of treatments that are already in use.

These and other topics will be the focus later this month of the 50th annual meeting of the American Association of Physicists in Medicine (AAPM), the largest medical physics association in the world. The meeting takes place from July 27 to July 31, in Houston, Texas.

Journalists are invited to cover the AAPM meeting in person or remotely. Additional news releases detailing other meeting highlights are hosted on the AAPM website (see link below).

-----SECTION ONE: CANCER RESEARCH HIGHLIGHTS IN BRIEF-----

1) BREAST CT SCANNERS PROMISE PAINLESS ALTERNATIVE TO MAMMOGRAPHY
"...The discomfort of a mammogram can drive some women to avoid the valuable screening, occasionally with dire consequences. Now a new procedure, dedicated breast computed tomography (CT), promises to take the pain out of breast cancer detection..." MORE DETAILS BELOW

2) MEASURING CANCER THERAPY SUCCESS WITH OXYGEN
"...Scientists at The Ohio State University (OSU) have identified a way to predict very early in the treatment process the outcome of radiation and chemotherapy for cervical cancer patients -- based on oxygen levels within the tumor..." MORE DETAILS BELOW

3) HYBRID IMAGER COULD IMPROVE BREAST EXAMS
"...An integrated, multi-modality molecular imaging system may improve detection, diagnosis and treatment monitoring of breast cancer, while also relieving some of the discomfort often associated with breast exams. The system allows subjects to lie prone while both a dedicated SPECT and CT scan are taken of the breast..." MORE DETAILS BELOW

4) SPARING LEUKEMIA PATIENTS FROM UNNECESSARY TREATMENT
"...Nearly a third of leukemia patients do not respond to chemotherapy, but this is not usually discovered until they have already endured a week-long chemotherapy treatment and waited a month to see whether it has worked. A new study shows that PET scans could tell how well a patient is responding after just one day of chemotherapy..." MORE DETAILS BELOW

5) OPTIMIZING THE TREATMENT OF SHALLOW TUMORS
"... A promising new way to treat superficial tumors, such as tumors of the scalp or of the chest wall after a mastectomy, is a procedure called modulated electron therapy (MERT). [Researchers] at the Washington University School of Medicine in St. Louis have developed a number of tools that make MERT more effective and customizable to individual patients..." MORE DETAILS BELOW

6) IN THE ZONE: USING LOW OXYGEN ZONES OF TUMORS TO GUIDE RADIATION THERAPY FOR HEAD AND NECK CANCERS
"...A familiar problem in cancer radiation therapy is the persistence of tumors that do not respond to standard doses. Tumors that are low in oxygen ("hypoxic") are in this category. They resist the curative effects of both radiation and chemotherapy-but that may change as a result of preliminary work by a group of New York researchers..." MORE DETAILS BELOW

7) STUDY CORRELATES TEMPORAL CHANGES IN TUMOR HETEROGENEITY TO TREATMENT RESPONSE
"...Some cancer cells may be highly resistant to radiation therapy, while others are insensitive to the drugs used in chemotherapy, all of which can confound cancer therapy. But does tumor heterogeneity change because of cancer treatment? [Researchers] at the University of Wisconsin, Madison, have taken the first steps toward finding an answer..." MORE DETAILS BELOW

8) NOVEL INSTRUMENT MAY IMPROVE UPON THE SAFETY AND EFFECTIVENESS OF CERVICAL CANCER BRACHYTHERAPY TREATMENTS
"... To treat cervical cancer, clinicians apply a high dose of radiation directly to diseased tissues, which may be administered using a device called an intracavitary brachytherapy applicator. Researchers at the M.D. Anderson Cancer Center have designed a new applicator made out of special materials that makes it compatible with MRIs, and features a movable shield that both reduces the exposure of healthy tissues to radiation and permits the use of CT and MRI scans..."MORE DETAILS BELOW

9) INNOVATIVE TECHNIQUE MAY ALLOW REAL-TIME IMAGING FOR PROTON THERAPY
"...One of the most effective means of treating cancers is via radiation therapy. However, ionization and its by-products damage both the cancer and normal cells...." MORE DETAILS BELOW

10) AUTOMATED COMPUTER ANALYSIS FOR DIAGNOSING BREAST CANCER
"... Ductal carcinoma in situ (DCIS), the development of cancer cells within the milk ducts of breast tissue, is thought to be a possible precursor of invasive cancer... Now researchers at the University of Chicago have developed an automated computer image analysis technique to ultimately characterize and diagnose DCIS and other breast carcinomas..." MORE DETAILS BELOW

11) TRACKING TUMORS WITH BATED BREATH
"...Breathing is a major complication for radiation treatment of lung cancer. The latest technology plans to tackle the problem by moving the radiation beam in unison with the breath. To help in the tracking, researchers have devised a new algorithm -- similar to one used by the post office -- that can predict where a tumor will be one second beforehand..." MORE DETAILS BELOW

-------SECTION TWO: FULL DETAILS ON SELECTED CANCER RESEARCH------

1) BREAST CT SCANNERS PROMISE PAINLESS ALTERNATIVE TO MAMMOGRAPHY

The discomfort of a mammogram can drive some women to avoid the valuable screening, occasionally with dire consequences. Now a new procedure, dedicated breast computed tomography (CT), promises to take the pain out of breast cancer detection.

In the cone beam breast CT scanner, which was first developed at the University of California, Davis, a woman lies face down on a special table with one breast suspended through an opening. A CT scanner rotates around the breast, collecting data that are reconstructed into a three-dimensional image. The total dose of radiation is the same as in a conventional mammogram.

Since 2004, the UC Davis researchers, led by John M. Boone (jmboone@ucdavis.edu), Professor and Vice Chair of Radiology and Professor of Biomedical Engineering, have scanned 160 women with their prototype scanner. In early 2008, the researchers began operating a second prototype device, into which the researchers have incorporated a positron emission tomography (PET) scanner. The PET scanner tracks the metabolic activity of a tumor, if present, so the hybrid CT/PET breast scanner would allow clinicians to, among other uses, precisely localize and monitor the response of a tumor to chemotherapy, determine the extent (or staging) of tumors, and help guide radiologists conducting biopsies.

The clinical trials show that the scanner "is better mammography for mass detection," Boone says, while "offering improved comfort to the patient and a better three-dimensional understanding of pathological lesions when they are present." The scanner, however, is less efficient than regular mammography at detecting the tiny clusters of calcium (or microcalcifications) that can sometimes signal breast cancer. This is because it uses X rays at higher energies than do mammograms, reducing the contrast of the images and the ability to distinguish the calcium clusters. "Thus, we are not making the claim that breast CT is "better" than mammography-yet," Boone says.

Talk (TU-D-342-04), "Dedicated Breast CT Imaging of the Breast" is at 2:45 p.m. on Tuesday, July 29, 2008 in room 342. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9957-68553-68.pdf.

2) MEASURING CANCER THERAPY SUCCESS WITH OXYGEN

Scientists at The Ohio State University (OSU) have identified a way to predict very early in the treatment process the outcome of radiation and chemotherapy for cervical cancer patients -- based on oxygen levels within the tumor.

The oxygenation of a tumor is critical for the success of cancer treatment. That's because the amount of oxygen in a cell is directly correlated with the ability of that cell to repair radiation damage. When the oxygen level is low, a state called hypoxia, the biological changes in tumor cells produced by radiation -- that will hopefully destroy the cells -- can be repaired, and tumor recurrence is more likely. But when oxygen is present, it reacts with free radical molecules to produce organic peroxide, which causes that damage to be "permanent and irreparable," says study head Jian Z. Wang, Ph.D. (wang.993@osu.edu), an Assistant Professor at OSU and the Director of the Radiation Response Modeling Program at the OSU James Cancer Hospital and Solove Research Institute. Inevitably, those well-oxygenated tumor cells die, tumors are less likely to return, and patient survival rates rise, says Wang.

In their study of 88 women with cervical cancer, Dr. Wang and his colleagues measured the level of hemoglobin, the oxygen-carrying molecule in blood, and measured blood supply to the tumor through magnetic resonance imaging (MRI) scans. Blood tests were conducted weekly beginning prior to treatment, and MRI scans were performed before radiation treatment, during radiation at 2-2.5 and 4-5 weeks, and 1-2 months after treatment. Cancer recurrence rates were tracked for up to 9 years. This study was supported by a NIH R01 grant led by the principal investigator Nina A. Mayr, M.D., Professor of Radiation Medicine at the OSU James Cancer Hospital and Solove Research Institute.

Measurements of tumor oxygenation just 2 weeks into treatment provided the best predictor of tumor control and disease-free survival. That early glimpse into the future can identify individuals at the greatest risk of having their cancer return, Mayr says, giving doctors the opportunity to adopt more aggressive therapies to improve the prognosis. Wang predicts that, with further testing, the technique also will prove useful for other types of cancer.

Talk (TH-D-AUD C-03), "When the Oxygen Level Matters Mostly During Radiation Therapy of Cervical Cancer?" is at 12:54 p.m. on Thursday July 31, 2008 in Auditorium C. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-8849-2782-979.pdf.

3) HYBRID IMAGER COULD IMPROVE BREAST EXAMS

An integrated, multi-modality molecular imaging system, invented in 1999 by Martin Tornai, Associate Professor of Radiology and Biomedical Engineering of Duke University, and developed by Priti Madhav (priti.madhav@duke.edu) and other of Tornai's grad students over the years, may improve detection, diagnosis and treatment monitoring of breast cancer, while also relieving some of the discomfort often associated with breast exams. The system allows subjects to lie prone while both a dedicated SPECT and CT scan are taken of the breast. Because these are three-dimensional imaging techniques, there is no need to compress the breast (often painfully) as is done during a two-dimensional mammography.

To generate the SPECT image, the nuclear medicine technologist injects the subject with a radio-tracer associated with metabolism. Cancer cells are more active than normal cells, so they take up more of the gamma-ray-emitting tracer. The SPECT camera detects this gamma ray emission and produces an image of the 3D distribution of metabolic activity. To help physically localize the source, a dedicated breast CT scan, also developed in Tornai's lab, with 0.5 millimeter resolution is obtained. When the two scans are fused together, the doctor has both functional (SPECT) and anatomical (CT) information in one picture. In a handful of patient imaging trials, the combined image highlighted cancerous cells that might have been missed in a CT scan by itself.

Although full body SPECT-CT already exists, this is the first dedicated SPECT-CT apparatus for breast imaging. The advantage of tailoring the machine to the breast is that the SPECT camera gets a better picture by being closer to the breast. Moreover, the CT scan is targeted, thus reducing the amount of radiation to other parts of the body. An added bonus is that the patient never has to move while the two scans are taken.

Talk (TU-C-332-04), "Pilot Patient Studies Using a Dedicated Dual-Modality SPECT-CT System for Breast Imaging" is at 10:36 a.m. on Tuesday, July 29, 2008 in room 332. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9680-20499-188.pdf.

4) SPARING LEUKEMIA PATIENTS FROM UNNECESSARY TREATMENT

Nearly a third of leukemia patients do not respond to chemotherapy, but this is not usually discovered until they have already endured a week-long chemotherapy treatment and waited a month to see whether it has worked. A new study shows that PET scans could tell how well a patient is responding after just one day of chemotherapy.

Treating leukemia primarily involves killing the cancerous cells where they originate in the bone marrow. Chemotherapy can knock out bone marrow cells, but it also kills healthy cells, causing such side effects as immunodeficiency and weight loss. Doctors traditionally take a bone marrow biopsy after the treatment to assess how well the drugs have worked. This is unfortunately rather late for those who do not respond to chemotherapy. And even for those who do, the single biopsy is not always representative of how the entire bone marrow is responding.

A PET scan can detect cancerous activity in a full-body image, but it had previously never been used to assess leukemia treatment. As an investigative study, Matt Vanderhoek (mattmv@gmail.com) of the University of Wisconsin and his colleagues imaged eight people with leukemia at different stages of their chemotherapy. They used a PET radio-tracer called FLT (fluoro-L-thymidine), which is readily taken up by cells during cell division. Since leukemia cells divide more than normal cells, they should absorb a lot of FLT and appear brighter in the bone marrow of a PET scan. However, if chemotherapy is able to kill these over-proliferative cells, then the bone marrow should appear dark.

In their sample, the researchers found that brightness and non-uniformity in bone marrow PET scans was an indication that the subject was not responding to the chemotherapy. This assessment, which apparently can be made as early as day one, could potentially spare 30 percent of people with leukemia from a treatment that is wrong for them.

Talk (TH-D-AUD C-6), "Early Assessment of Treatment Response in Hematopoietic Disease Using [18F]FLT PET Imaging " is at 1:30 p.m. on Thursday July 29, 2008 in Auditorium C. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-8912-11242-598.pdf.

5) OPTIMIZING THE TREATMENT OF SHALLOW TUMORS

A promising new way to treat superficial tumors, such as tumors of the scalp or of the chest wall after a mastectomy, is a procedure called modulated electron therapy (MERT). That's because the radiation dose of an electron beam falls off rapidly with distance, which allows the tumor to be irradiated at doses sufficient to kill cancerous cells, but spares the healthy tissue beneath from exposure to too much radiation.

Murat Surucu (msurucu@radonc.wustl.edu), a Postdoctoral Research Associate in the Radiation Oncology Department at the Washington University School of Medicine in St. Louis, and his colleagues have developed a number of tools that make MERT more effective and customizable to individual patients. Their protocol includes an automated field-shaping method to modulate the intensity of the electron beam and improve the ability to deliver an appropriate dosage to the tumor, a graphic user interface that can modify automated fields and energy selection, simulations that calculate dose distribution, and a second graphical user interface to optimize the overall dose distribution in the patient.

Surucu is the winner of the Jack Fowler Junior Investigator Competition, established in honor of Jack Fowler, Emeritus Professor of Human Oncology and Medical Physics at the University of Wisconsin. Talk (MO-D-351-01), "Optimization Tools for Modulated Electron Radiotherapy" is at 1:30 p.m. on Monday, July 28, 2008 in room 351. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9488-86182-982.pdf.

6) IN THE ZONE: USING LOW OXYGEN ZONES OF TUMORS TO GUIDE RADIATION THERAPY FOR HEAD AND NECK CANCERS

A familiar problem in cancer radiation therapy is the persistence of tumors that do not respond to standard doses. Tumors that are low in oxygen ("hypoxic") are in this category. They resist the curative effects of both radiation and chemotherapy-but that may change as a result of preliminary work by a group of New York researchers.

While much research is devoted to molecular manipulations to reverse or block the hypoxic tumor-promoting environment, the New York team is taking a new tactic: They are using the low-oxygen chemical signal to guide an adjustable-strength radiation treatment called Intensity Modulated Radiation Therapy (IMRT). The intensity modulation approach not only uses the low-oxygen environment to locate zones of radiation resistance, it then delivers extra radiation doses to the zones in hopes of overcoming resistance to standard doses. Researchers can also scale back the dose to minimize damage to tissues characterized by normal oxygen levels.

N. Lee, M.D. (leen2@mskcc.org), from Memorial Sloan-Kettering Cancer Center in New York, is the lead researcher. She explains the significance of the team's work this way: "Our results are able to visualize variable levels of hypoxia within tumors, which is potentially important for future therapies because it suggests this is a feasible approach to locating pockets of resistance and gaining local control over head and neck cancers."

Dr. Lee's group tested this approach in 10 patients with head and neck cancer. To visualize the tumors' oxygen environments they radioactively labeled tracers and gave them intravenously to patients. The tracers were detected and displayed as an image by a technology known as 18F-fluoromisonidazole positron emission tomography (PET) scanning. Low oxygen zones were revealed based on a tumor zone's uptake of the tracers. Regions of elevated 18F-fluoromisonidazole were identified as low in oxygen, and then treated with an intensity-modulated radiation boost to overcome the resistant zones.

Talk (WE-D-AUD C-2), "Hypoxia-Guided Intensity-Modulated Radiation Therapy for Head and Neck Cancer" is at 1:30 p.m. on Wednesday, July 30, 2008 in Auditorium C. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9784-92744-669.pdf.

7) STUDY CORRELATES TEMPORAL CHANGES IN TUMOR HETEROGENEITY TO TREATMENT RESPONSE

Tumors are notoriously heterogeneous. Although the cells of a tumor may descend from the same progenitor cell, they can mutate to become genetically unique, displaying distinct characteristics and behavior, and responding differently to environmental assaults. Some cancer cells, for example, may be highly resistant to radiation therapy, while others are insensitive to the drugs used in chemotherapy, all of which can confound cancer therapy. But does tumor heterogeneity change because of cancer treatment?

Chihwa Song (csong1@wisc.edu), a postdoctoral researcher in the Department of Medical Physics at the University of Wisconsin, Madison, has with his colleagues taken the first steps toward finding an answer. The scientists conducted a statistical analysis of heterogeneity and its progression in nine people undergoing radiotherapy and six people getting chemotherapy, for various types of cancer. Each patient underwent diagnostic imaging prior to, and during, treatment.

Using a special type of positron emission tomography scan, the researchers looked for variation within tumors in the rates at which clumps of cells proliferate, which could be visualized as clusters of rapidly growing cells. A rapid rate of cell proliferation is one characteristic of highly malignant tumors. Song and colleagues found no major changes in proliferation heterogeneity over the course of radiotherapy treatment, but a large decrease in the amount of heterogeneity during chemotherapy. A larger decrease in heterogeneity could mean that the patients were becoming more responsive to their treatment.

The study, Song says, "seems to show that tumor heterogeneity changes over the time course of treatment, with response to treatment related to that change," although the reasons why remain unclear. "If this is true, a change in tumor heterogeneity will serve as a prognostic tool."

Talk (TH-D-AUD C-05), "Assessment of Heterogeneity Change in Tumors over Time Course of Treatment" is at 1:18 p.m. on Thursday July 31, 2008 in Auditorium C. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9117-60820-214.pdf.

8) NOVEL INSTRUMENT MAY IMPROVE UPON THE SAFETY AND EFFECTIVENESS OF CERVICAL CANCER BRACHYTHERAPY TREATMENTS

To treat cervical cancer, clinicians apply a high dose of radiation directly to diseased tissues, which may be administered using a device called an intracavitary brachytherapy applicator. Imaging the treated areas using computerized tomography (CT) or magnetic resonance imaging (MRI) improves the effectiveness of treatments because the scans allow clinicians to accurately plan the radiation treatments. But when so-called "shielded" applicators, which contain metal shields to protect healthy bladder and rectal tissues from radiation exposure, are used to deliver these treatments, CT images exhibit distortion. Furthermore, the devices themselves are not compatible with MRI scanners.

A new design avoids those problems. The applicator was invented and developed by the faculty at the M.D. Anderson Cancer Center and evaluated by Ph.D. medical physics candidate, Michael J. Price (mjprice@mdanderson.org) for his dissertation work under the direction of Firas Mourtada, Ph.D. It is made out of special materials that makes it compatible with MRIs, and features a movable shield that both reduces the exposure of healthy tissues to radiation and permits the use of CT and MRI scans. Because the shield can be moved out of the path of the scanners' beams, the applicator can be used in conjunction with CT without distortion to the images. In addition, Price says, "the position of the shield can be adjusted as a function of specific patient anatomy," allowing clinicians to tailor treatments for each individual patient. Preliminary studies by the MD Anderson team show that the device may reduce the radiation dose to the rectum by 22% when compared to a commonly used CT/MRI-compatible intracavitary brachytherapy applicator.

Talk (SU-H-AUD C-10), "The Imaging and Dosimetric Capabilities of a Novel CT/MR-Suitable, Anatomically Adaptive, Shielded HDR/PDR Intracavitary Brachytherapy Applicator for the Treatment of Cervical Cancer" is at 5:48 p.m. on Sunday, July 28, 2008. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9284-60990-964.pdf.

9) INNOVATIVE TECHNIQUE MAY ALLOW REAL-TIME IMAGING FOR PROTON THERAPY

One of the most effective means of treating cancers is via radiation therapy. However, ionization and its by-products damage both the cancer and normal cells. Accuracy and precision of the radiation delivered to the tumor and the ability to spare normal tissue determine patient outcomes. Recently, high energy proton beams have been shown to be more precise in delivering energy to the tumor than photon beams, but even with advanced treatment planning, the delivery of the beam to the tumor may deviate from the treatment plan due to the complications of the anatomy and motion of patients.

The ability to see the location and measure the amount of energy delivered during the treatment in real time would allow radiation oncologists to adjust the energy delivered to the tumor assuring that the prescribed energy is delivered at right location. Since high energy protons and photons induce gamma rays via interaction with nuclei in the human body by imaging the gamma rays, one could see the location and measure the amount of energy delivered during treatment. Unfortunately, the penetration power of the emitted gamma rays is too high to be stopped and imaged with conventional medical imaging modalities in real time.

Using principles adapted from gamma ray astronomy, a research team at the University of Florida is working to develop a modality capable of imaging the gamma rays in 3D. The team has designed an imager using a new material, LaBr3, with high stopping power. The researchers are now optimizing the design and doing bench-top testing, which has demonstrated the feasibility of this concept with a precision of about 5mm at 10 cm distance.

As the next step, the team will prototype and test the imager in radiation therapy clinical facilities using proton and photon beams. Dr. Yuxin Feng, a member of the Florida team, believes that the challenge of accelerating image reconstruction speed to achieve real or near real time imaging is achievable with the development of image reconstruction and computing power, making real-time imaging in proton therapy a reality.

Talk (TU-D-352-3), "A Design of Compton Cameras for Imaging Gamma Emission in Proton Therapy" is at 1:54 p.m. on Tuesday July 29, 2008 in Room 352. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9435-45230-12.pdf

10) AUTOMATED COMPUTER ANALYSIS FOR DIAGNOSING BREAST CANCER

Ductal carcinoma in situ (DCIS), the development of cancer cells within the milk ducts of breast tissue, is thought to be a possible precursor of invasive cancer, prompting research to understand its underlying biology-and detect it early. Now medical physics graduate student Neha Bhooshan (bhooshan@uchicago.edu) of the University of Chicago, her advisor Professor Maryellen Giger, and their colleagues have developed an automated computer image analysis technique to ultimately characterize and diagnose DCIS and other breast carcinomas.

The method is similar to the computer-aided detection techniques currently used to identify suspicious features on mammograms for further study by radiologists. It makes use of differences in the morphology of DCIS and other malignant and benign breast lesions, and in their response to the contrast agents used in magnetic resonance imaging (MRI) scans. For example, malignant and benign breast lesions vary in the rates at which they take in and eliminate MRI contrast agents; malignant lesions rapidly take in and wash out the contrast because they have a greater proliferation of blood vessels, while benign lesions have a slow and persistent uptake. The computer program compares seven such features in breast MRI scans taken before and after the administration of contrast, and calculates a numerical value that characterizes the tumor subtype.

To test the program's validity, the researchers used it to analyze MRI scans of 131 benign and 203 malignant breast lesions, including 79 lesions that had been pathologically diagnosed as DCIS and 124 as invasive ductal carcinoma (IDC). The system was able to differentiate benign and malignant lesions, and to distinguish DCIS and IDC lesions. Bhooshan believes computer-aided diagnosis can be applied to the image analysis of other types of cancer and may become more common in the clinical setting.

Talk (SU-HH-AUD C-07), "Classification of Breast Carcinoma Subtypes Using Computer-Extracted Morphological and Kinetic Features in DCE-MRI" is at 5:12 p.m. on Sunday, July 26, 2008 in Auditorium C. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-8548-9547-137.pdf.

11) TRACKING TUMORS WITH BATED BREATH

Breathing is a major complication for radiation treatment of lung cancer. The latest technology plans to tackle the problem by moving the radiation beam in unison with the breath. To help in the tracking, researchers have devised a new algorithm -- similar to one used by the post office -- that can predict where a tumor will be one second beforehand.

Breathing is a problem in radiation treatment not only for lung cancer, but also for cancers in other parts of the abdomen. Medical physicists have traditionally dealt with this motion by shooting a beam that broadly covers the area in which the tumor is located. Because there will be plenty of healthy tissue inside this big margin of error, the beam strength has to be turned down low.

A better way to treat cancer is to use intense, highly-focused beams that only strike the tumor. This is why the next generation of radiation treatments have robotic arms or special shutters that can move the beam up and down to stay centered on a moving target. But these new techniques will require a precise way to track where the tumor is inside the chest.

Nadeem Riaz (nadeem.riaz@gmail.com) and collaborators at Stanford University School of Medicine have a model that accurately predicts a tumor's motion using its last eight positions. The algorithm, which improves its performance by learning from its mistakes, is also used by the post office to automatically read zip codes on letters. The researchers tested their program on data from a previous radiation treatment in which a tumor was tracked with X-ray images and found it worked better than another simple model at predicting where the tumor will be one second into the future. One second should be enough time, Riaz says, for newly-developed technologies to redirect their radiation beams.

Talk (TH-C-AUD C-07), "Prediction of Fiducial Motion in Respiratory Tumors for Image-Guided Radiotherapy" is at 11:12 a.m. on Thursday July 31, 2008 in Auditorium C. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9656-50294-757.pdf.

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ABOUT AAPM
The American Association of Physicists in Medicine (AAPM) is a scientific, educational, and professional nonprofit organization whose mission is to advance the application of physics to the diagnosis and treatment of human disease. 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. In 2008, AAPM will celebrate its 50th year of serving patients, physicians, and physicists. Please visit the association's Web site at http://www.aapm.org/.

Media contacts:
Jason Socrates Bardi, American Institute of Physics,
301-209-3091 (office) 858-775-4080 (cell)
jbardi@aip.org

Jeff Limmer, AAPM Media Relations Subcommittee Chair
jeffl@aspirus.org



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