title: A deliverable four-dimensional intensity-modulated radiation therapy-planning method for dynamic multileaf collimator tumor tracking delivery.
abstract: OBJECTIVE
  To develop a deliverable four-dimensional (4D) intensity-modulated radiation therapy (IMRT) planning method for dynamic multileaf collimator (MLC) tumor tracking delivery.
  
  
  METHODS
  The deliverable 4D IMRT planning method involves aligning MLC leaf motion parallel to the major axis of target motion and translating MLC leaf positions by the difference in the target centroid position between respiratory phases of the 4D CT scan. This method ignores nonlinear respiratory motion and deformation. A three-dimensional (3D) optimal method whereby an IMRT plan on each respiratory phase of the 4D CT scan was independently optimized was used for comparison. For 12 lung cancer patient 4D CT scans, individual phase plans and deformable dose-summed 4D plans using the two methods were created and compared.
  
  
  RESULTS
  For each of the individual phase plans, the deliverable method yielded similar isodose distributions and dose-volume histograms. The deliverable and 3D optimal methods yielded statistically equivalent dose-volume metrics for both individual phase plans and 4D plans (p > 0.05 for all metrics compared). The deliverable method was affected by 4D CT artifacts in one case. Both methods were affected by high vector field variations from deformable registration.
  
  
  CONCLUSIONS
  The deliverable method yielded similar dose distributions for each of the individual phase plans and statistically equivalent dosimetric values compared with the 3D optimal method, indicating that the deliverable method is dosimetrically robust to the variations of fractional time spent in respiratory phases on a given 4D CT scan. Nonlinear target motion and deformation did not cause significant dose discrepancies.
authors.affiliation: Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA, USA. ysuh@stanford.edu
authors.forename: Yelin
authors.initials: Y
authors.lastname: Suh
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Weiss
authors.forename: Hualiang
authors.initials: H
authors.lastname: Zhong
authors.forename: Mirek
authors.initials: M
authors.lastname: Fatyga
authors.forename: Jeffrey V
authors.initials: JV
authors.lastname: Siebers
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Keall
mesh_terms: D016477:Artifacts; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D009068:Movement; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation / Q000379:methods*; D012119:Respiration; D014057:Tomography, X-Ray Computed / Q000379:methods