title: Target tracking using DMLC for volumetric modulated arc therapy: a simulation study.
abstract: OBJECTIVE
  Target tracking using dynamic multileaf collimator (DMLC) is a promising approach for intrafraction motion management in radiation therapy. The purpose of this work is to develop a DMLC tracking algorithm capable of delivering volumetric-modulated arc therapy (VMAT) to the targets that experience two-dimensional (2D) rigid motion in the beam's eye view.
  
  
  METHODS
  The problem of VMAT delivery to moving targets is formulated as a control problem with constraints. The relationships between gantry speed, gantry acceleration, MLC leaf-velocity, dose rate, and target motion are derived. An iterative search algorithm is developed to find numerical solutions for efficient delivery of a specific VMAT plan to the moving target using 2D DMLC tracking. The delivery of five VMAT lung plans is simulated. The planned and delivered fluence maps in the target-reference frame are calculated and compared.
  
  
  RESULTS
  The simulation demonstrates that the 2D tracking algorithm is capable of delivering the VMAT plan to a moving target fast and accurately without violating the machine constraints and the integrity of the treatment plan. The average delivery time is only 29 s longer than that of no-tracking delivery, 101 versus 72 s, respectively. The fluence maps are normalized to 200 MU and the average root-mean-square error between the desired and the delivered fluence is 2.1 MU, compared to 14.8 MU for no-tracking and 3.6 MU for one-dimensional tracking.
  
  
  CONCLUSIONS
  A locally optimal MLC tracking algorithm for VMAT delivery is proposed, aiming at shortest delivery time while maintaining treatment plan invariant. The inconsequential increase of treatment time due to DMLC tracking is clinically desirable, which makes VMAT with DMLC tracking attractive in treating moving tumors.
authors.affiliation: Department of Radiation Oncology, School of Medicine, Washington University, 4921 Parkview Place, St. Louis, Missouri 63110, USA.
authors.forename: Baozhou
authors.initials: B
authors.lastname: Sun
authors.forename: Dharanipathy
authors.initials: D
authors.lastname: Rangaraj
authors.forename: Lech
authors.initials: L
authors.lastname: Papiez
authors.forename: Swetha
authors.initials: S
authors.lastname: Oddiraju
authors.forename: Deshan
authors.initials: D
authors.lastname: Yang
authors.forename: H Harold
authors.initials: HH
authors.lastname: Li
mesh_terms: D000465:Algorithms; D019583:Dose Fractionation, Radiation; D006801:Humans; D009068:Movement; D011881:Radiotherapy, Computer-Assisted / Q000379:methods*; D012119:Respiration; D012984:Software