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HOUSTON MEETING HIGHLIGHTS: Physics and the Future of Medicine
American Association of Physicists in Medicine Meeting, July 27 to July 31

2. MIXED BEAM THERAPY MAY OFFER ADVANTAGES FOR TREATMENT OF SHALLOW TUMORS

Recent work by team of researchers from M.D. Anderson Cancer Center, the Mayo Clinic, and Louisiana State University may bring clinicians closer to the use of mixed beam therapy, which would combine electron and x-ray beams and improve therapeutic outcomes in people with shallow tumors.

Intensity-modulated x-ray therapy (IMRT) is a clinical technique that delivers radiation to the tumor volume and spares normal tissues, while an x-ray multi-leaf collimator is used to help "match" the dose distribution to complex tumor shapes. Mixed-beam therapy combines both intensity-modulated electron and x-ray beams using an x-ray multi-leaf collimator to improve target coverage and sparing of critical structures, particularly for cancers of the head, neck and breast. This is possible since the dose from electron beams is reduced quickly as it penetrates through the patient so that there is almost no dose exiting the patient. Using an x-ray multi-leaf collimator to modulate the intensity of electron beams is advantageous because the hardware needed is already available on most existing linear accelerators, though collaboration with the manufacturers of linear accelerators would be required to implement the mixed-beams technique in the clinic.

The mixed-beam technique could be used for people with tumors close to the skin surface, such as parotid, ear or sinus tumors for head and neck patients and in most breast cases. Mixed beam therapy reduces dose to normal tissue resulting in fewer negative side effects, which may lead to fewer secondary malignancies in the future.

Dr. Rebecca Weinberg (RWEINBERG@swmail.sw.org) has taken the first step in realizing the potential of mixed-beam therapy with an x-ray multi-leaf collimator. "There were many other ways of approaching the mixed-beams treatment planning that I was unable to explore due to time constraints and limitation of the currently-available treatment planning software," explains Weinberg. Further research is needed to optimize the mixed electron and x-ray dose distributions, especially reducing dose calculation and clinical treatment delivery times to offer cancer patients the best possible outcome.

Talk (TH-D-AUD B-5), "Electron Intensity Modulation for Mixed-Beam Radiation Therapy with An X-Ray Multi-Leaf Collimator" is at 1:18 p.m. on Thursday, July 31, 2008 in Auditorium B. Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9349-94925-545.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/.

ABOUT AIP

Headquartered in College Park, MD., the American Institute of Physics is a not-for-profit membership corporation chartered in New York State in 1931 for the purpose of promoting the advancement and diffusion of the knowledge of physics and its application to human welfare.

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