title: Daily alignment results of in-room computed tomography-guided stereotactic body radiation therapy for lung cancer.
abstract: OBJECTIVE
  To determine the extent of interfractional setup errors and day-to-day organ motion errors by assessing daily bone alignment results and changes in soft tissue tumor position during hypofractionated, in-room computed tomography (CT)-guided stereotactic body radiation therapy (SBRT) of lung cancer.
  
  
  METHODS
  Daily alignment results during SBRT were analyzed for 117 tumors in 112 patients. Patients received 40-50 Gy of SBRT in four to five fractions using an integrated CT-LINAC system. The free-breathing CT scans acquired during treatment setup were retrospectively realigned to match with each of the bony references and the gross tumor volume (GTV) defined on the reference CT by rigid-body registration, and the daily deviations were calculated.
  
  
  RESULTS
  The mean magnitude (± SD) three-dimensional shift from the initial skin marks to the final bone-aligned positions was 9.4 ± 5.7 mm. The mean daily GTV deviation from the bone position was 0.1 ± 3.8 mm in the anterior-posterior direction, -0.01 ± 4.2 mm in the superior-inferior direction, and 0.2 ± 2.5 mm in the lateral direction. A clinically noteworthy trend (net change >5 mm in any direction) in GTV position relative to the bone was observed in 23 cases (20%).
  
  
  CONCLUSIONS
  Soft tissue target position can change significantly beyond the motion envelope defined in the original internal target volume in four-dimensional CT-based treatment planning for SBRT of lung cancer. Additional margin should be considered for adequate coverage of interfractional changes.
authors.affiliation: Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Ikushima
authors.forename: Peter
authors.initials: P
authors.lastname: Balter
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Komaki
authors.forename: Sandeep
authors.initials: S
authors.lastname: Hunjun
authors.forename: M Kara
authors.initials: MK
authors.lastname: Bucci
authors.forename: Zhongxing
authors.initials: Z
authors.lastname: Liao
authors.forename: Mary F
authors.initials: MF
authors.lastname: McAleer
authors.forename: Zhiqian H
authors.initials: ZH
authors.lastname: Yu
authors.forename: Yongbin
authors.initials: Y
authors.lastname: Zhang
authors.forename: Joe Y
authors.initials: JY
authors.lastname: Chang
authors.forename: Lei
authors.initials: L
authors.lastname: Dong
mesh_terms: D001842:Bone and Bones / Q000000981:diagnostic imaging; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D008297:Male; D009068:Movement; D016634:Radiosurgery / Q000379:methods*; D011881:Radiotherapy, Computer-Assisted / Q000379:methods; D015203:Reproducibility of Results; D012189:Retrospective Studies; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000379:methods*; D047368:Tumor Burden