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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

5. RESEARCHERS QUANTIFY SECONDARY RISKS OF PROTON THERAPY

Researchers from M.D. Anderson Cancer Center and the Georgia Institute of Technology have completed a study that will help people considering proton therapy for cancer treatment and the physicians who treat them. While proton therapy offers great advantages over traditional radiation therapy by delivering radiation dose to the tumor volume while sparing the adjacent healthy tissue/organ, there was concern that secondary neutrons produced along the proton path in the treatment machine and inside the patient could give unwanted dose and pose risks for secondary malignancies.

Prior to this study, there has been very limited measured data of neutron spectrum and dose equivalent from proton therapy in the literature due to the difficulty in measuring high-energy neutrons. However, this team of scientists used a method sensitive to neutrons ranging from thermal energy to 1 GeV to measure the neutron spectral dose equivalent around a mini-phantom using a proton beam simulating treatment typical for children, in order to determine neutron dose equivalent from proton irradiation. It was also critical for the researchers to determine how much of the neutron dose equivalent was generated inside the body since neutrons from the treatment head can be reduced by using low-neutron-generating material, shielding, or scanning beam technique, while neutrons produced inside the body cannot be reduced.

Results showed a maximum neutron dose equivalent of less than 1% of the prescribed proton dose, a low enough dose that it should not be a concern even for children receiving proton therapy. In addition, the major contribution was from neutrons produced in the treatment head, which can be mitigated by using several available techniques. This should provide radiation oncologists confidence that proton irradiation can be used to treat people with cancer, including children, without worrying about secondary malignancies. This also makes a compelling case for new scanned beam proton therapy as compared with passive scattering beam.

Talk (Th-D-AUD-A2), "Measurement of Neutron Spectrum and Ambient Dose Equivalent Around a Mini-Phantom at a Proton Therapy Facility" is at 12:42 p.m. on Thursday July 31, 2008. Contact: Z Wang (zlwang@mdanderson.org). Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9559-78392-720.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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Jason Socrates Bardi, American Institute of Physics,
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