By a News Reporter-Staff News Editor at Biotech Week -- Current study results on Medical Physics have been published. According to news originating from Ann Arbor, Michigan, by NewsRx correspondents, research stated, "To present and characterize a measurement technique to quantify the calibration accuracy of an electromagnetic tracking system to radiation isocenter. This technique was developed as a quality assurance method for electromagnetic tracking systems used in a multi-institutional clinical hypofractionated prostate study."
Our news journalists obtained a quote from the research from the University of Michigan, "In this technique, the electromagnetic tracking system is calibrated to isocenter with the manufacturers recommended technique, using laser-based alignment. A test patient is created with a transponder at isocenter whose position is measured electromagnetically. Four portal images of the transponder are taken with collimator rotations of 45 degrees 135 degrees, 225 degrees, and 315 degrees, at each of four gantry angles (0 degrees, 90 degrees, 180 degrees, 270 degrees) using a 3 x 6 cm(2) radiation field. In each image, the center of the copper-wrapped iron core of the transponder is determined. All measurements are made relative to this transponder position to remove gantry and imager sag effects. For each of the 16 images, the 50% collimation edges are identified and used to find a ray representing the rotational axis of each collimation edge. The 16 collimator rotation rays from four gantry angles pass through and bound the radiation isocenter volume. The center of the bounded region, relative to the transponder, is calculated and then transformed to tracking system coordinates using the transponder position, allowing the tracking system's calibration offset from radiation isocenter to be found. All image analysis and calculations are automated with inhouse software for user-independent accuracy. Three different tracking systems at two different sites were evaluated for this study. The magnitude of the calibration offset was always less than the manufacturer's stated accuracy of 0.2 cm using their standard clinical calibration procedure, and ranged from 0.014 to 0.175 cm. On three systems in clinical use, the magnitude of the offset was found to be 0.053 +/- 0.036, 0.121 +/- 0.023, and 0.093 +/- 0.013 cm. The method presented here provides an independent technique to verify the calibration of an electromagnetic tracking system to radiation isocenter. The calibration accuracy of the system was better than the 0.2 cm accuracy stated by the manufacturer."
According to the news editors, the research concluded: "However, it should not be assumed to be zero, especially for stereotactic radiation therapy treatments where planning target volume margins are very small."
For more information on this research see: A measurement technique to determine the calibration accuracy of an electromagnetic tracking system to radiation isocenter. Medical Physics, 2013;40(8):189-196. Medical Physics can be contacted at: Amer Assoc Physicists Medicine Amer Inst Physics, Ste 1 No 1, 2 Huntington Quadrangle, Melville, NY 11747-4502, USA. (American Association of Physicists in Medicine - www.aapm.org; Medical Physics - online.medphys.org/)
The news correspondents report that additional information may be obtained from D.W. Litzenberg, University of Michigan, Dept. of Radiat Oncol, Ann Arbor, MI 48109, United States. Additional authors for this research include I. Gallagher, K.J. Masi, C. Lee, J.I. Prisciandaro, D.A. Hamstra, T. Ritter and K.L. Lam (see also Medical Physics).
Keywords for this news article include: Michigan, Ann Arbor, United States, Medical Physics, Radiation Therapy, North and Central America
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