title: Respiration induced heart motion and indications of gated delivery for left-sided breast irradiation.
abstract: OBJECTIVE
  To investigate respiration-induced heart motion for left-sided breast irradiation using a four-dimensional computed tomography (4DCT) technique and to determine novel indications to assess heart motion and identify breast patients who may benefit from a gated treatment.
  
  
  METHODS
  Images of 4DCT acquired during free breathing for 20 left-sided breast cancer patients, who underwent whole breast irradiation with or without regional nodal irradiation, were analyzed retrospectively. Dose distributions were reconstructed in the phases of 0%, 20%, and 50%. The intrafractional heart displacement was measured in three selected transverse CT slices using D(LAD) (the distance from left ascending aorta to a fixed line [connecting middle point of sternum and the body] drawn on each slice) and maximum heart depth (MHD, the distance of the forefront of the heart to the line). Linear regression analysis was used to correlate these indices with mean heart dose and heart dose volume at different breathing phases.
  
  
  RESULTS
  Respiration-induced heart displacement resulted in observable variations in dose delivered to the heart. During a normal free-breathing cycle, heart-induced motion D(LAD) and MHD changed up to 9 and 11 mm respectively, resulting in up to 38% and 39% increases of mean doses and V(25.2) for the heart. MHD and D(LAD) were positively correlated with mean heart dose and heart dose volume. Respiratory-adapted gated treatment may better spare heart and ipsilateral-lung compared with the conventional non-gated plan in a subset of patients with large D(LAD) or MHD variations.
  
  
  CONCLUSIONS
  Proposed indices offer novel assessment of heart displacement based on 4DCT images. MHD and D(LAD) can be used independently or jointly as selection criteria for respiratory gating procedure before treatment planning. Patients with great intrafractional MHD variations or tumor(s) close to the diaphragm may particularly benefit from the gated treatment.
authors.affiliation: Department of Radiation Oncology, University of Colorado Denver, Aurora, CO, USA. xiangrong.qi@ucdenver.edu
authors.forename: X Sharon
authors.initials: XS
authors.lastname: Qi
authors.forename: Angela
authors.initials: A
authors.lastname: Hu
authors.forename: Kai
authors.initials: K
authors.lastname: Wang
authors.forename: Francis
authors.initials: F
authors.lastname: Newman
authors.forename: Marcus
authors.initials: M
authors.lastname: Crosby
authors.forename: Bin
authors.initials: B
authors.lastname: Hu
authors.forename: Julia
authors.initials: J
authors.lastname: White
authors.forename: X Allen
authors.initials: XA
authors.lastname: Li
mesh_terms: D059925:Anatomic Landmarks / Q000000981:diagnostic imaging; D001011:Aorta; D001027:Aortography; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D019583:Dose Fractionation, Radiation; D005260:Female; D056973:Four-Dimensional Computed Tomography; D006321:Heart / Q000000981:diagnostic imaging* / Q000528:radiation effects; D006801:Humans; D009068:Movement; D011832:Radiation Injuries / Q000517:prevention & control; D012119:Respiration; D055425:Respiratory-Gated Imaging Techniques / Q000379:methods; D012189:Retrospective Studies