Hindawi Publishing Corporation Prostate Cancer Volume 2012, Article ID 130579, 6 pages doi:10.1155/2012/130579 Research Article Prostate Intrafraction Translation Margins for Real-Time Monitoring and Correction Strategies Dale W. Litzenberg, 1 James M. Balter, 1 Scott W. Hadley, 1 Daniel A. Hamstra, 1 Twyla R. Willoughby, 2 Patrick A. Kupelian, 3 Toufik Djemil, 4 Arul Mahadevan, 4 Shirish Jani, 5 Geoffrey Weinstein, 5 Timothy Solberg, 6 Charles Enke, 7 Lisa Levine, 8 and Howard M. Sandler 9 1 Department of Radiation Oncology, University of Michigan Health System, Ann Arbor, MI 48109-5010, USA 2 M. D. Anderson Cancer Center Orlando, Orlando, FL 32806, USA 3 UCLA, Los Angeles, CA 90095, USA 4 Cleveland Clinic Foundation, Cleveland, OH 44195, USA 5 Sharp Health Care Hospital, San Diego, CA 92123, USA 6 University of Texas Southwestern Medical Center, Dallas, TX 75390, USA 7 Nebraska Medical Center, Omaha, NE 68198, USA 8 Calypso Medical Technologies Inc., Seattle, WA 98121, USA 9 Cedars-Sinai, Los Angeles, CA 90048, USA Correspondence should be addressed to Dale W. Litzenberg, litzen@umich.edu Received 25 January 2011; Accepted 12 May 2011 Academic Editor: May Abdel-Wahab Copyright © 2012 Dale W. Litzenberg et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The purpose of this work is to determine appropriate radiation therapy beam margins to account for intrafraction prostate translations for use with real-time electromagnetic position monitoring and correction strategies. Motion was measured continuously in 35 patients over 1157 fractions at 5 institutions. This data was studied using van Herk’s formula of (αΣ + γσ ′ ) for situations ranging from no electromagnetic guidance to automated real-time corrections. Without electromagnetic guidance, margins of over 10mm are necessary to ensure 95% dosimetric coverage while automated electromagnetic guidance allows the margins necessary for intrafraction translations to be reduced to submillimeter levels. Factors such as prostate deformation and rotation, which are not included in this analysis, will become the dominant concerns as margins are reduced. Continuous electromagnetic monitoring and automated correction have the potential to reduce prostate margins to 2-3mm, while ensuring that a higher percentage of patients (99% versus 90%) receive a greater percentage (99% versus 95%) of the prescription dose. 1. Introduction The goal of conformal radiation therapy is to shape the dose distribution to the prescribed target volume as closely as pos- sible without sacrificing target coverage. This technique results in the sparing of neighboring healthy tissues and often leads to fewer complications and higher quality of life. It may also allow higher doses to target volumes that are limited by toxicity of normal tissues, potentially resulting in better local tumor control. In the last five years, real-time electromagnet- ic tracking of the prostate has become commercially available and has been adopted as the preferred localization technique in many clinics where it is available. The technology makes it possible to essentially eliminate interfraction variations, greatly reduces systematic uncertainties, and allows intra- fraction target volume motion to be monitored continuously throughout treatment so that corrective adaptive action may be taken. A description of the Calypso System has been previously reported [1, 2]. Briefly, the system consists of a tracking sta- tion (placed in the control room) to display real-time devia- tions for the target volume from isocenter. Ceiling-mounted