title: Residual setup errors and dose variations with less-than-daily image guided patient setup in external beam radiotherapy for esophageal cancer.
abstract: OBJECTIVE
  To evaluate residual patient setup errors and daily dose variations of different less-than-daily image guidance (IG) strategies in the delivery of external beam radiotherapy for esophageal cancer.
  
  
  METHODS
  Daily image-guided setup data for 25 consecutive esophageal cancer patients treated with helical tomotherapy were evaluated. Seven less-than-daily IG strategies with different imaging frequencies were simulated. For each IG strategy, the daily residual setup errors were calculated. Using TomoTherapy Planned Adaptive software, daily dose variations to the clinical target volume, heart, and lungs were evaluated in five representative patients.
  
  
  RESULTS
  With 0% (60%) IG frequency, the margins required for adequate coverage of the clinical target volume were 13 mm (10 mm), 14 mm (11 mm), and 5 mm (5 mm) in the left-right, superior-inferior, and anterior-posterior directions, respectively. Even with 60% IG frequency, 10% of the fractions had more than 10% decrease in the dose level covering 95% of the target, and 14% and 13% of the fractions had more than 10% increase in total lung volume receiving at least 0.8 Gy per fraction, and heart volume receiving at least 1.2 Gy per fraction, respectively.
  
  
  CONCLUSIONS
  Substantial residual setup errors would occur for treatment fractions without IG even if the most frequent less-than-daily IG strategy was to be used, which could lead to significant daily dose variations for the target volume and adjacent normal tissues. Daily image guidance is recommended throughout the course of treatment in conformal radiotherapy for esophageal cancer.
authors.affiliation: Department of Radiation Oncology, City of Hope National Medical Center, Duarte, CA 91010, USA. chan@coh.org
authors.forename: Chunhui
authors.initials: C
authors.lastname: Han
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Schiffner
authors.forename: Timothy E
authors.initials: TE
authors.lastname: Schultheiss
authors.forename: Yi-Jen
authors.initials: YJ
authors.lastname: Chen
authors.forename: An
authors.initials: A
authors.lastname: Liu
authors.forename: Jeffrey Y C
authors.initials: JY
authors.lastname: Wong
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019583:Dose Fractionation, Radiation; D004938:Esophageal Neoplasms / Q000532:radiotherapy*; D005260:Female; D006321:Heart / Q000528:radiation effects; D006801:Humans; D008168:Lung / Q000528:radiation effects; D008297:Male; D008875:Middle Aged; D058958:Organs at Risk; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061106:Radiotherapy Setup Errors; D020266:Radiotherapy, Conformal / Q000379:methods*; D012984:Software; D036542:Tomography, Spiral Computed