title: Dosimetric effect of translational and rotational errors for patients undergoing image-guided stereotactic body radiotherapy for spinal metastases.
abstract: OBJECTIVE
  To investigate the dosimetric effects of translational and rotational patient positioning errors on the treatment of spinal and paraspinal metastases using computed tomography image-guided stereotactic body radiotherapy. The results of this study provide guidance for the treatment planning process and recognition of the dosimetric consequences of daily patient treatment setup errors.
  
  
  METHODS
  The data from 20 patients treated for metastatic spinal cancer using image-guided stereotactic body radiotherapy were investigated in this study. To simulate the dosimetric effects of residual setup uncertainties, 36 additional plans (total, 756 plans) were generated for each isocenter (total, 21 isocenters) on the planning computed tomography images, which included isocenter lateral, anteroposterior, superoinferior shifts, and patient roll, yaw, and pitch rotations. Tumor volume coverage and the maximal dose to the organs at risk were compared with those of the original plan. Six daily treatments were also investigated to determine the dosimetric effect with or without the translational and rotational corrections.
  
  
  RESULTS
  A 2-mm error in translational patient positioning error in any direction can result in >5% tumor coverage loss and >25% maximal dose increase to the organs at risk. Rotational correction is very important for patients with multiple targets and for the setup of paraspinal patients when the isocenter is away from bony structures. Compared with the original plans, the daily treatment data indicated that translational adjustments could correct most of the setup errors to mean divergences of -1.4% for tumor volume coverage and -0.3% for the maximal dose to the organs at risk.
  
  
  CONCLUSIONS
  For the best dosimetric results, spinal stereotactic treatments should have setup translational errors of < or =1 mm and rotational errors of < or =2 degrees .
authors.affiliation: Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, TX 77030-4009, USA. hewang@manderson.org
authors.forename: He
authors.initials: H
authors.lastname: Wang
authors.forename: Almon
authors.initials: A
authors.lastname: Shiu
authors.forename: Congjun
authors.initials: C
authors.lastname: Wang
authors.forename: Jennifer
authors.initials: J
authors.lastname: O'Daniel
authors.forename: Anita
authors.initials: A
authors.lastname: Mahajan
authors.forename: Shiao
authors.initials: S
authors.lastname: Woo
authors.forename: Praimakorn
authors.initials: P
authors.lastname: Liengsawangwong
authors.forename: Radhe
authors.initials: R
authors.lastname: Mohan
authors.forename: Eric L
authors.initials: EL
authors.lastname: Chang
mesh_terms: D016477:Artifacts; D006801:Humans; D009068:Movement; D016634:Radiosurgery / Q000379:methods*; D011879:Radiotherapy Dosage; D015203:Reproducibility of Results; D012399:Rotation; D012680:Sensitivity and Specificity; D013125:Spinal Neoplasms / Q000175:diagnosis / Q000532:radiotherapy* / Q000556:secondary*; D025321:Surgery, Computer-Assisted / Q000379:methods*