title: Electromagnetic-guided dynamic multileaf collimator tracking enables motion management for intensity-modulated arc therapy.
abstract: OBJECTIVE
  Intensity-modulated arc therapy (IMAT) is attractive because of high-dose conformality and efficient delivery. However, managing intrafraction motion is challenging for IMAT. The purpose of this research was to develop and investigate electromagnetically guided dynamic multileaf collimator (DMLC) tracking as an enabling technology to treat moving targets during IMAT.
  
  
  METHODS
  A real-time three-dimensional DMLC-based target tracking system was developed and integrated with a linear accelerator. The DMLC tracking software inputs a real-time electromagnetically measured target position and the IMAT plan, and dynamically creates new leaf positions directed at the moving target. Low- and high-modulation IMAT plans were created for lung and prostate cancer cases. The IMAT plans were delivered to a three-axis motion platform programmed with measured patient motion. Dosimetric measurements were acquired by placing an ion chamber array on the moving platform. Measurements were acquired with tracking, without tracking (current clinical practice), and with the phantom in a static position (reference). Analysis of dose distribution differences from the static reference used a γ-test.
  
  
  RESULTS
  On average, 1.6% of dose points for the lung plans and 1.2% of points for the prostate plans failed the 3-mm/3% γ-test with tracking; without tracking, 34% and 14% (respectively) of points failed the γ-test. The delivery time was the same with and without tracking.
  
  
  CONCLUSIONS
  Electromagnetic-guided DMLC target tracking with IMAT has been investigated for the first time. Dose distributions to moving targets with DMLC tracking were significantly superior to those without tracking. There was no loss of treatment efficiency with DMLC tracking.
authors.affiliation: Department of Radiation Oncology, Stanford University, Stanford, CA 94305-5847, USA. keall@stanford.edu
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Keall
authors.forename: Amit
authors.initials: A
authors.lastname: Sawant
authors.forename: Byungchul
authors.initials: B
authors.lastname: Cho
authors.forename: Dan
authors.initials: D
authors.lastname: Ruan
authors.forename: Junqing
authors.initials: J
authors.lastname: Wu
authors.forename: Per
authors.initials: P
authors.lastname: Poulsen
authors.forename: Jay
authors.initials: J
authors.lastname: Petersen
authors.forename: Laurence J
authors.initials: LJ
authors.lastname: Newell
authors.forename: Herbert
authors.initials: H
authors.lastname: Cattell
authors.forename: Stine
authors.initials: S
authors.lastname: Korreman
mesh_terms: D004574:Electromagnetic Fields; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D008297:Male; D009068:Movement; D010315:Particle Accelerators; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000601:surgery*; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation / Q000379:methods*