title: [Study of feasibility of verifying setup errors for patients with head tumor by observing patients' SSD].
abstract: OBJECTIVE
  To verify the feasibility of setup error verification by observing patents' source-skin distance (SSD) for patients of head tumor.
  
  
  METHODS
  Films for 21 patients with head tumor were recorded using simulator (Varian Acuity 8.6), and comparison with reference digitally reconstructed radiograph (DRR) from Treatment plan system (TPS). The deviation of setup for 21 patients in the left-right, anterior-posterior and superior-inferior directions were measured by using 2D match, and SSD error was recorded when gantry angle was 0 degrees, 45 degrees, 315 degrees. Then setup error and corresponding SSD error were analyzed.
  
  
  RESULTS
  The systematic errors and random errors of 21 patients in the left-right, anterior-posterior and superior-inferior directions were (1.1 +/- 11.6) mm, (0.7 +/- 1.2) mm, (0.9 +/- 1.5) mm, and (1.51 +/- 3.1) mm, (1.05 +/- 3.3) mm, (1.60 +/- 2.3) mm. The systematic SSD errors and random SSD errors were (1.25 +/- 1.3) mm, (1.04 +/- 1.3) mm. (1.10 +/- 2.3) mm, and (2.03 +/- 1.7) mm, (2.81 +/- 2.3) mm, (2.33 +/- 3.0) mm for gantry angle was 0 degrees, 45 degrees, 315 degrees, respectively.
  
  
  CONCLUSIONS
  It is simple and feasible for setup error verification by observing patients' SSD and can be auxiliary to other verification means.
authors.affiliation: Department of Radiation Oncology, First Affiliated Hospital of Anhui Medical University, Hefei, 230022.
authors.forename: Cui
authors.initials: C
authors.lastname: Enping
authors.forename: Wang
authors.initials: W
authors.lastname: Zhi
authors.forename: Tang
authors.initials: T
authors.lastname: Hong
mesh_terms: D000465:Algorithms; D001918:Brachytherapy / Q000379:methods*; D005240:Feasibility Studies; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted