title: Impact of a large breast separation on radiation dose delivery to the ipsilateral lung as result of respiratory motion quantified using free breathing and 4D CT-based planning in patients with locally advanced breast cancers: a potential for adverse clinical implications.
abstract: OBJECTIVE
  We examined the effects of large breast separation (BS) on dosimetric and positional differences of radiation treatment plans of locally advanced breast cancers during a free-breathing respiratory cycle.
  
  
  METHODS
  Computed tomography (CT) datasets of 18 patients were acquired using 3D, 4D-0% (end-inspiration), and 4D-50% (end-exhalation). BS was examined in relation to the positional and dosimetric changes to organs-at-risk (OAR). Based on dosimetric analysis of all three plans, we compared 4D-0% and 4D-50% for V5, V10, and V20 to 3D for heart and ipsilateral lung. Using 4D-0% and 4D-50% CTs, we recorded positional variations of the organs' centroid (centers of mass) and their effects on dosimetry.
  
  
  RESULTS
  Median BS was 23.95 cm (range: 16.86-29.48 cm). There was a strong positive correlation between BS and dose to the ipsilateral lung for V5, V10, and V20, with the greatest linearity observed at V20 (R(2) = 0.23). At BS ≥ 27 cm, the dose increased during inspiration at V5, V10 , and V20 (P < 0.05). When comparing 4D and 3D for the heart, V5 and V10, decreased by average of 0.94% and 0.96% (P < 0.008), respectively.
  
  
  CONCLUSIONS
  This study offers the first evidence of the impact of a large BS on radiation dose to the ipsilateral lung.
authors.affiliation: Department of Radiation Oncology, Stich Radiation Center, NewYork-Presbyterian Hospital, Weill Cornell Medical Center, New York, NY 10065, USA.
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Heineman
authors.forename: Albert
authors.initials: A
authors.lastname: Sabbas
authors.forename: Marilynn Santos
authors.initials: MS
authors.lastname: Delamerced
authors.forename: Ya-lin
authors.initials: YL
authors.lastname: Chiu
authors.forename: Michael
authors.initials: M
authors.lastname: Smith
authors.forename: Bhupesh
authors.initials: B
authors.lastname: Parashar
authors.forename: A Gabriella
authors.initials: AG
authors.lastname: Wernicke
mesh_terms: D000328:Adult; D001940:Breast / Q000033:anatomy & histology*; D001943:Breast Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D005260:Female; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging* / Q000528:radiation effects*; D008875:Middle Aged; D009367:Neoplasm Staging; D009929:Organ Size; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000009:adverse effects