title: Verification of planning target volume settings in volumetric modulated arc therapy for stereotactic body radiation therapy by using in-treatment 4-dimensional cone beam computed tomography.
abstract: OBJECTIVE
  To evaluate setup error and tumor motion during beam delivery by using 4-dimensional cone beam computed tomography (4D CBCT) and to assess the adequacy of the planning target volume (PTV) margin for lung cancer patients undergoing volumetric modulated arc therapy for stereotactic body radiation therapy (VMAT-SBRT).
  
  
  METHODS
  Fifteen lung cancer patients treated by single-arc VMAT-SBRT were selected in this analysis. All patients were treated with an abdominal compressor. The gross tumor volumes were contoured on maximum inspiration and maximum expiration CT datasets from 4D CT respiratory sorting and merged into internal target volumes (ITVs). The PTV margin was isotropically taken as 5 mm. Registration was automatically performed using "pre-3D" CBCT. Treatment was performed with a D95 prescription of 50 Gy delivered in 4 fractions. The 4D tumor locations during beam delivery were determined using in-treatment 4D CBCT images acquired in each fraction. Then, the discrepancy between the actual tumor location and the ITV was evaluated in the lateral, vertical, and longitudinal directions.
  
  
  RESULTS
  Overall, 55 4D CBCT sets during VMAT-SBRT were successfully obtained. The amplitude of tumor motion was less than 10 mm in all directions. The average displacements between ITV and actual tumor location during treatment were 0.41 ± 0.93 mm, 0.15 ± 0.58 mm, and 0.60 ± 0.99 mm for the craniocaudal, left-right, and anteroposterior directions, respectively. The discrepancy in each phase did not exceed 5 mm in any direction.
  
  
  CONCLUSIONS
  With in-treatment 4D CBCT, we confirmed the required PTV margins when the registration for moving target was performed using pre-3D CBCT. In-treatment 4D CBCT is a direct method for quantitatively assessing the intrafractional location of a moving target.
authors.affiliation: Department of Radiology, The University of Tokyo Hospital, Tokyo, Japan.
authors.forename: Wataru
authors.initials: W
authors.lastname: Takahashi
authors.forename: Hideomi
authors.initials: H
authors.lastname: Yamashita
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kida
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Masutani
authors.forename: Akira
authors.initials: A
authors.lastname: Sakumi
authors.forename: Kuni
authors.initials: K
authors.lastname: Ohtomo
authors.forename: Keiichi
authors.initials: K
authors.lastname: Nakagawa
authors.forename: Akihiro
authors.initials: A
authors.lastname: Haga
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D019583:Dose Fractionation, Radiation; D005260:Female; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D009068:Movement; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061106:Radiotherapy Setup Errors; D061089:Radiotherapy, Image-Guided / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012119:Respiration; D047368:Tumor Burden