title: Electromagnetic real-time tumor position monitoring and dynamic multileaf collimator tracking using a Siemens 160 MLC: geometric and dosimetric accuracy of an integrated system.
abstract: OBJECTIVE
  Dynamic multileaf collimator tracking represents a promising method for high-precision radiotherapy to moving tumors. In the present study, we report on the integration of electromagnetic real-time tumor position monitoring into a multileaf collimator-based tracking system.
  
  
  METHODS
  The integrated system was characterized in terms of its geometric and radiologic accuracy. The former was assessed from portal images acquired during radiation delivery to a phantom in tracking mode. The tracking errors were calculated from the positions of the tracking field and of the phantom as extracted from the portal images. Radiologic accuracy was evaluated from film dosimetry performed for conformal and intensity-modulated radiotherapy applied to different phantoms moving on sinusoidal trajectories. A static radiation delivery to the nonmoving target served as a reference for the delivery to the moving phantom with and without tracking applied.
  
  
  RESULTS
  Submillimeter tracking accuracy was observed for two-dimensional target motion despite the relatively large system latency of 500 ms. Film dosimetry yielded almost complete recovery of a circular dose distribution with tracking in two dimensions applied: 2%/2 mm gamma-failure rates could be reduced from 59.7% to 3.3%. For single-beam intensity-modulated radiotherapy delivery, accuracy was limited by the finite leaf width. A 2%/2 mm gamma-failure rate of 15.6% remained with tracking applied.
  
  
  CONCLUSIONS
  The integrated system we have presented marks a major step toward the clinical implementation of high-precision dynamic multileaf collimator tracking. However, several challenges such as irregular motion traces or a thorough quality assurance still need to be addressed.
authors.affiliation: Department of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany. andreas.krauss@dkfz-heidelberg.de
authors.forename: Andreas
authors.initials: A
authors.lastname: Krauss
authors.forename: Simeon
authors.initials: S
authors.lastname: Nill
authors.forename: Martin
authors.initials: M
authors.lastname: Tacke
authors.forename: Uwe
authors.initials: U
authors.lastname: Oelfke
mesh_terms: D004574:Electromagnetic Fields; D004581:Electronics; D004867:Equipment Design; D057918:Fiducial Markers; D005373:Film Dosimetry / Q000379:methods; D009068:Movement; D010315:Particle Accelerators / Q000295:instrumentation*; D019047:Phantoms, Imaging; D020266:Radiotherapy, Conformal / Q000295:instrumentation / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation* / Q000379:methods