title: On the dose to a moving target while employing different IMRT delivery mechanisms.
abstract: OBJECTIVE
  To compare the temporal uniformity in dose delivered to a moving target for various intensity modulation radiotherapy (IMRT) modalities: solid intensity modulator (SIM), segmented multi-leaf collimator (SMLC), and dynamic multi-leaf collimator (DMLC).
  
  
  METHODS
  Two separate four-dimensional computed tomography data sets were obtained. Tumor motion kernels and motion envelopes were determined from composite positions of the tumor in various phases of the breathing cycle. Treatment plans were created for an unmodulated open field, SIM, SMLC, and DMLC. The motion envelope was treated as a static target volume. A robotic apparatus equipped with a diode array simulated the tumor motion in the plane of the beam's eye view (BEV). Radiation was delivered to the moving target over ten trials for each modality. The average coefficient of variation (CV) was determined for each beam angle.
  
  
  RESULTS
  The CV ranged from 0.09% to 0.15%, 0.23% to 3.14%, 1.14% to 5.51%, and 3.83% to 8.25% for the unmodulated open field, SIM, SMLC, and DMLC modalities, respectively. With gating, the CV was 0.23% to 2.31%, 0.31% to 2.97%, and 0.7% to 4.67% for SIM, SMLC, and DMLC, respectively.
  
  
  CONCLUSIONS
  SIM consistently provided the most temporally uniform dose to the moving target while DMLC provided the least. The SMLC and DMLC CV improved with gated delivery.
authors.affiliation: Department of Medical Physics, University of Wisconsin, Madison, WI 53792, USA.
authors.forename: Eric D
authors.initials: ED
authors.lastname: Ehler
authors.forename: Benjamin E
authors.initials: BE
authors.lastname: Nelms
authors.forename: Wolfgang A
authors.initials: WA
authors.lastname: Tomé
mesh_terms: D003198:Computer Simulation; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D009068:Movement; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012119:Respiration