title: Geometrical uncertainty of heart position in deep-inspiration breath-hold radiotherapy of left-sided breast cancer patients.
abstract: BACKGROUND
  This study aimed to determine the geometrical uncertainty of the position of the heart with daily cone beam computed tomography (CBCT) during deep-inspiration breath-hold (DIBH) treatment of the left breast.
  
  
  METHODS
  A visually guided optical respiratory monitoring system was used in DIBH treatment of 15 breast cancer patients. Heart position was determined in relation to the planning target volume (PTV) in 225 fractions in which daily low-dose CBCT images were compared with planning CT images. In addition, the position of the left lung apex and diaphragm was measured to evaluate the success of the DIBH.
  
  
  RESULTS
  The median shift of the heart was 1 mm to the left, 1 mm superiorly and 0 mm in the anterior-posterior (AP) direction during the treatment course when compared to the PTV position in planning CT. Based on these movements, an AP margin of 4 mm, a lateral (LR) margin of 3 mm, and a superior-inferior (SI) margin of 5 mm should be added to the heart contour to ensure avoiding the heart when planning treatment. The distance between the left lung apex and diaphragm, applied as a surrogate for lung volume, was 2mm (median) smaller during the CBCT acquisitions than during the planning CT acquisition. The correlation coefficient between the surrogate of lung volume and the distance between the heart and PTV was r = .46 in the AP, r = .72 in the LR and r = .79 in the SI directions.
  
  
  CONCLUSIONS
  Residual variation was observed in the position of the heart in comparison to PTV, even with a visually guided DIBH technique. These geometrical uncertainties should be taken into account when planning radiotherapy treatment. The success of DIBH may make a major contribution to the variation of the heart position during treatment.
authors.affiliation: a Cancer Center, Kuopio University Hospital , Kuopio , Finland.|b Department of Radiation Therapy , Central Finland Central Hospital , Jyväskylä , Finland.
authors.forename: Tuomas
authors.initials: T
authors.lastname: Koivumäki
authors.affiliation: c Department of Applied Physics , University of Eastern Finland , Kuopio , Finland.
authors.forename: Juuso
authors.initials: J
authors.lastname: Tujunen
authors.affiliation: a Cancer Center, Kuopio University Hospital , Kuopio , Finland.|c Department of Applied Physics , University of Eastern Finland , Kuopio , Finland.
authors.forename: Tuomas
authors.initials: T
authors.lastname: Virén
authors.affiliation: a Cancer Center, Kuopio University Hospital , Kuopio , Finland.
authors.forename: Janne
authors.initials: J
authors.lastname: Heikkilä
authors.affiliation: a Cancer Center, Kuopio University Hospital , Kuopio , Finland.
authors.forename: Jan
authors.initials: J
authors.lastname: Seppälä
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D062485:Breath Holding / Q000528:radiation effects*; D054893:Cone-Beam Computed Tomography / Q000379:methods; D005260:Female; D006321:Heart / Q000528:radiation effects; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008875:Middle Aged; D058958:Organs at Risk / Q000528:radiation effects*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods; D035501:Uncertainty; D000069584:Unilateral Breast Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*