title: Integration of real-time internal electromagnetic position monitoring coupled with dynamic multileaf collimator tracking: an intensity-modulated radiation therapy feasibility study.
abstract: OBJECTIVE
  Continuous tumor position measurement coupled with a tumor tracking system would result in a highly accurate radiation therapy system. Previous internal position monitoring systems have been limited by fluoroscopic radiation dose and low delivery efficiency. We aimed to incorporate a continuous, electromagnetic, three-dimensional position tracking system (Calypso 4D Localization System) with a dynamic multileaf collimator (DMLC)-based dose delivery system.
  
  
  METHODS
  A research version of the Calypso System provided real-time position of three Beacon transponders. These real-time three-dimensional positions were sent to research MLC controller with a motion-tracking algorithm that changed the planned leaf sequence. Electromagnetic transponders were embedded in a solid water film phantom that moved with patient lung trajectories while being irradiated with two different plans: a step-and-shoot intensity-modulated radiation therapy (S-IMRT) field and a dynamic IMRT (D-IMRT) field. Dosimetric results were recorded under three conditions: no intervention, DMLC tracking, and a spatial gating system.
  
  
  RESULTS
  Dosimetric accuracy was comparable for gating and DMLC tracking. Failure rates for gating/DMLC tracking are as follows: +/-3 cGy 10.9/ 7.5% for S-IMRT, 3.3/7.2% for D-IMRT; gamma (3mm/3%) 0.2/1.2% for S-IMRT, 0.2/0.2% for D-IMRT. DMLC tracking proved to be as efficient as standard delivery, with a two- to fivefold efficiency increase over gating.
  
  
  CONCLUSIONS
  Real-time target position information was successfully integrated into a DMLC effector system to modify dose delivery. Experimental results show both comparable dosimetric accuracy as well as improved efficiency compared with spatial gating.
authors.affiliation: Washington University Saint Louis, Saint Louis, MO 63110, USA.
authors.forename: Ryan L
authors.initials: RL
authors.lastname: Smith
authors.forename: Amit
authors.initials: A
authors.lastname: Sawant
authors.forename: Lakshmi
authors.initials: L
authors.lastname: Santanam
authors.forename: Raghu B
authors.initials: RB
authors.lastname: Venkat
authors.forename: Laurence J
authors.initials: LJ
authors.lastname: Newell
authors.forename: Byung-Chul
authors.initials: BC
authors.lastname: Cho
authors.forename: Per
authors.initials: P
authors.lastname: Poulsen
authors.forename: Herbert
authors.initials: H
authors.lastname: Catell
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Keall
authors.forename: Parag J
authors.initials: PJ
authors.lastname: Parikh
mesh_terms: D000465:Algorithms; D003199:Computer Systems; D004867:Equipment Design; D005240:Feasibility Studies; D008175:Lung Neoplasms / Q000532:radiotherapy; D009068:Movement; D010315:Particle Accelerators / Q000295:instrumentation* / Q000592:standards; D019047:Phantoms, Imaging; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation* / Q000379:methods / Q000592:standards