title: Effect of breast volume on treatment reproducibility on a tomotherapy unit in the treatment of breast cancer.
abstract: OBJECTIVE
  To determine whether the volume of a patient's breast is correlated with reliable daily setup in treatment of breast cancer with a helical tomotherapy treatment unit.
  
  
  METHODS
  Thirty-six consecutive patients with breast cancer were treated on a helical tomotherapy unit. During simulation, kilovoltage CT images were obtained for treatment planning. These were fused with daily megavoltage CT scans, and after setup based on skin marks and laser alignment the necessary shifts were carried out. The magnitude of daily shifts (in millimeters) was retrospectively obtained from the daily image fusions, and the breast volume was obtained from the treatment plan. A total of 873 fusion scans were reviewed. Random error for absolute and directional daily shifts was evaluated for correlation to volume. Variation over time was also evaluated.
  
  
  RESULTS
  Mean (SD) random shift for all patients in the lateral, longitudinal, and vertical directions was 2.7 (2.0), 3.1 (1.5), and 3.2 (2.6) mm, respectively. Mean (SD) absolute distance shifted was 6.0 (3.5) mm. There was no significant correlation between mean absolute or mean directional daily shift and breast volume (0.08, 0.08, 0.22, and 0.07, respectively). There was no correlation between setup variation and time.
  
  
  CONCLUSIONS
  In this cohort, there was no correlation between breast volume and degree of daily shift. There was no correlation between time course and setup variation. Therefore, setup variation does not improve or degrade with repeated treatment setups.
authors.affiliation: Department of Radiation Oncology, University of Cincinnati, Cincinnati, OH 45267, USA. offermsn@ucmail.uc.edu
authors.forename: Shannon
authors.initials: S
authors.lastname: Offerman
authors.forename: Michael
authors.initials: M
authors.lastname: Lamba
authors.forename: Ruth
authors.initials: R
authors.lastname: Lavigne
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001940:Breast / Q000033:anatomy & histology*; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D008327:Mammography; D008875:Middle Aged; D009068:Movement; D009929:Organ Size; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D015203:Reproducibility of Results; D012189:Retrospective Studies