title: Couch-based motion compensation: modelling, simulation and real-time experiments.
abstract: The paper presents a couch-based active motion compensation strategy evaluated in simulation and validated experimentally using both a research and a clinical Elekta Precise Table™. The control strategy combines a Kalman filter to predict the surrogate motion used as a reference by a linear model predictive controller with the control action calculation based on estimated position and velocity feedback provided by an observer as well as predicted couch position and velocity using a linearized state space model. An inversion technique is used to compensate for the dead-zone nonlinearity. New generic couch models are presented and applied to model the Elekta Precise Table™ dynamics and nonlinearities including dead zone. Couch deflection was measured for different manufacturers and found to be up to 25 mm. A feed-forward approach is proposed to compensate for such couch deflection. Simultaneous motion compensation for longitudinal, lateral and vertical motions was evaluated using arbitrary trajectories generated from sensors or loaded from files. Tracking errors were between 0.5 and 2 mm RMS. A dosimetric evaluation of the motion compensation was done using a sinusoidal waveform. No notable differences were observed between films obtained for a fixed- or motion-compensated target. Further dosimetric improvement could be made by combining gating, based on tracking error together with beam on/off time, and PSS compensation.
authors.affiliation: Control Theory and Applications Centre, Coventry University, Priory Street, Coventry CV1 5FB, UK.
authors.forename: Olivier C L
authors.initials: OCL
authors.lastname: Haas
authors.affiliation: Water Software Systems, DeMontfort University, 00.26 Hawthorn Building, The Gateway, Leicester LE1 9BH, UK.
authors.forename: Piotr
authors.initials: P
authors.lastname: Skworcow
authors.affiliation: Water Software Systems, DeMontfort University, 00.26 Hawthorn Building, The Gateway, Leicester LE1 9BH, UK.
authors.forename: Daniel
authors.initials: D
authors.lastname: Paluszczyszyn
authors.affiliation: Control Theory and Applications Centre, Coventry University, Priory Street, Coventry CV1 5FB, UK.
authors.forename: Abdelhamid
authors.initials: A
authors.lastname: Sahih
authors.affiliation: Control Theory and Applications Centre, Coventry University, Priory Street, Coventry CV1 5FB, UK.
authors.forename: Mariusz
authors.initials: M
authors.lastname: Ruta
authors.affiliation: Control Theory and Applications Centre, Coventry University, Priory Street, Coventry CV1 5FB, UK.|Radiotherapy Physics Manager, University Hospital, Clifford Bridge Rd, Coventry CV2 2DX UK.
authors.forename: John A
authors.initials: JA
authors.lastname: Mills
mesh_terms: D006801:Humans; D008962:Models, Theoretical; D009068:Movement; D056888:Patient Positioning; D011881:Radiotherapy, Computer-Assisted / Q000295:instrumentation*; D013997:Time Factors