title: 4D Proton treatment planning strategy for mobile lung tumors.
abstract: OBJECTIVE
  To investigate strategies for designing compensator-based 3D proton treatment plans for mobile lung tumors using four-dimensional computed tomography (4DCT) images.
  
  
  METHODS
  Four-dimensional CT sets for 10 lung cancer patients were used in this study. The internal gross tumor volume (IGTV) was obtained by combining the tumor volumes at different phases of the respiratory cycle. For each patient, we evaluated four planning strategies based on the following dose calculations: (1) the average (AVE) CT; (2) the free-breathing (FB) CT; (3) the maximum intensity projection (MIP) CT; and (4) the AVE CT in which the CT voxel values inside the IGTV were replaced by a constant density (AVE_RIGTV). For each strategy, the resulting cumulative dose distribution in a respiratory cycle was determined using a deformable image registration method.
  
  
  RESULTS
  There were dosimetric differences between the apparent dose distribution, calculated on a single CT dataset, and the motion-corrected 4D dose distribution, calculated by combining dose distributions delivered to each phase of the 4DCT. The AVE_RIGTV plan using a 1-cm smearing parameter had the best overall target coverage and critical structure sparing. The MIP plan approach resulted in an unnecessarily large treatment volume. The AVE and FB plans using 1-cm smearing did not provide adequate 4D target coverage in all patients. By using a larger smearing value, adequate 4D target coverage could be achieved; however, critical organ doses were increased.
  
  
  CONCLUSIONS
  The AVE_RIGTV approach is an effective strategy for designing proton treatment plans for mobile lung tumors.
authors.affiliation: Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030-4009, USA.
authors.forename: Yixiu
authors.initials: Y
authors.lastname: Kang
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Zhang
authors.forename: Joe Y
authors.initials: JY
authors.lastname: Chang
authors.forename: He
authors.initials: H
authors.lastname: Wang
authors.forename: Xiong
authors.initials: X
authors.lastname: Wei
authors.forename: Zhongxing
authors.initials: Z
authors.lastname: Liao
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Komaki
authors.forename: James D
authors.initials: JD
authors.lastname: Cox
authors.forename: Peter A
authors.initials: PA
authors.lastname: Balter
authors.forename: Helen
authors.initials: H
authors.lastname: Liu
authors.forename: X Ronald
authors.initials: XR
authors.lastname: Zhu
authors.forename: Radhe
authors.initials: R
authors.lastname: Mohan
authors.forename: Lei
authors.initials: L
authors.lastname: Dong
mesh_terms: D006801:Humans; D007091:Image Processing, Computer-Assisted; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D009068:Movement; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D014057:Tomography, X-Ray Computed; D011522:Protons
chemical_list: D011522:Protons