IOP PUBLISHING PHYSICS IN MEDICINE AND BIOLOGY Phys. Med. Biol. 52 (2007) 4137–4153 doi:10.1088/0031-9155/52/14/008 Formulating adaptive radiation therapy (ART) treatment planning into a closed-loop control framework * Adam de la Zerda 1 , Benjamin Armbruster 2 and Lei Xing 3 1 Department of Electrical Engineering, Stanford University, Stanford, CA 94305-9505, USA 2 Department of Management Science and Engineering, Stanford University, Stanford, CA 94305-4026, USA 3 Department of Radiation Oncology, Stanford University, Stanford, CA 94305-5847, USA E-mail: lei@reyes.stanford.edu Received 17 January 2007, in final form 25 April 2007 Published 14 June 2007 Online at stacks.iop.org/PMB/52/4137 Abstract While ART has been studied for years, the specific quantitative implementation details have not. In order for this new scheme of radiation therapy (RT) to reach its potential, an effective ART treatment planning strategy capable of taking into account the dose delivery history and the patient’s on-treatment geometric model must be in place. This paper performs a theoretical study of dynamic closed-loop control algorithms for ART and compares their utility with data from phantom and clinical cases. We developed two classes of algorithms: those Adapting to Changing Geometry and those Adapting to Geometry and Delivered Dose. The former class takes into account organ deformations found just before treatment. The latter class optimizes the dose distribution accumulated over the entire course of treatment by adapting at each fraction, not only to the information just before treatment about organ deformations but also to the dose delivery history. We showcase two algorithms in the class of those Adapting to Geometry and Delivered Dose. A comparison of the approaches indicates that certain closed-loop ART algorithms may significantly improve the current practice. We anticipate that improvements in imaging, dose verification and reporting will further increase the importance of adaptive algorithms. (Some figures in this article are in colour only in the electronic version) 1. Introduction Current IMRT treatment plan optimization and dose delivery are two decoupled steps (AAPM IMRT Sub-committee 2003, Webb 2001). In each fraction, the patient geometry is hardly the * Presented at ASTRO Annual Meeting, 2006, Philadelphia, PA. 0031-9155/07/144137+17$30.00 © 2007 IOP Publishing Ltd Printed in the UK 4137