title: An image-guided study of setup reproducibility of postmastectomy breast cancer patients treated with inverse-planned intensity modulated radiation therapy.
abstract: OBJECTIVE
  To calculate planning target volume (PTV) margins for chest wall and regional nodal targets using daily orthogonal kilovolt (kV) imaging and to study residual setup error after kV alignment using volumetric cone-beam computed tomography (CBCT).
  
  
  METHODS
  Twenty-one postmastectomy patients were treated with intensity modulated radiation therapy with 7-mm PTV margins. Population-based PTV margins were calculated from translational shifts after daily kV positioning and/or weekly CBCT data for each of 8 patients, whose surgical clips were used as surrogates for target volumes. Errors from kV and CBCT data were mathematically combined to generate PTV margins for 3 simulated alignment workflows: (1) skin marks alone; (2) weekly kV imaging; and (3) daily kV imaging.
  
  
  RESULTS
  The kV data from 613 treatment fractions indicated that a 7-mm uniform margin would account for 95% of daily shifts if patients were positioned using only skin marks. Total setup errors incorporating both kV and CBCT data were larger than those from kV alone, yielding PTV expansions of 7 mm anterior-posterior, 9 mm left-right, and 9 mm superior-inferior. Required PTV margins after weekly kV imaging were similar in magnitude as alignment to skin marks, but rotational adjustments of patients were required in 32% ± 17% of treatments. These rotations would have remained uncorrected without the use of daily kV imaging. Despite the use of daily kV imaging, CBCT data taken at the treatment position indicate that an anisotropic PTV margin of 6 mm anterior-posterior, 4 mm left-right, and 8 mm superior-inferior must be retained to account for residual errors.
  
  
  CONCLUSIONS
  Cone-beam CT provides additional information on 3-dimensional reproducibility of treatment setup for chest wall targets. Three-dimensional data indicate that a uniform 7-mm PTV margin is insufficient in the absence of daily IGRT. Interfraction movement is greater than suggested by 2-dimensional imaging, thus a margin of at least 4 to 8 mm must be retained despite the use of daily IGRT.
authors.affiliation: Department of Radiation and Cellular Oncology, The University of Chicago, Chicago, Illinois.
authors.forename: Christine H
authors.initials: CH
authors.lastname: Feng
authors.affiliation: Department of Radiation and Cellular Oncology, The University of Chicago, Chicago, Illinois.
authors.forename: Emily
authors.initials: E
authors.lastname: Gerry
authors.affiliation: Department of Radiation and Cellular Oncology, The University of Chicago, Chicago, Illinois.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Chmura
authors.affiliation: Department of Radiation and Cellular Oncology, The University of Chicago, Chicago, Illinois.
authors.forename: Yasmin
authors.initials: Y
authors.lastname: Hasan
authors.affiliation: Department of Radiation and Cellular Oncology, The University of Chicago, Chicago, Illinois. Electronic address: hal-hallaq@radonc.uchicago.edu.
authors.forename: Hania A
authors.initials: HA
authors.lastname: Al-Hallaq
mesh_terms: D000328:Adult; D000368:Aged; D015415:Biomarkers; D001943:Breast Neoplasms / Q000532:radiotherapy* / Q000601:surgery; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D005260:Female; D006801:Humans; D015182:Lymphatic Irradiation / Q000379:methods; D008408:Mastectomy; D008875:Middle Aged; D011182:Postoperative Care; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061106:Radiotherapy Setup Errors; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D015203:Reproducibility of Results; D012399:Rotation; D013525:Surgical Instruments; D035441:Thoracic Wall; D055815:Young Adult
chemical_list: D015415:Biomarkers