title: Monitoring ABC-assisted deep inspiration breath hold for left-sided breast radiotherapy with an optical tracking system.
abstract: OBJECTIVE
  Recent knowledge on the effects of cardiac toxicity warrants greater precision for left-sided breast radiotherapy. Different breath-hold (BH) maneuvers (abdominal vs thoracic breathing) can lead to chest wall positional variations, even though the patient's tidal volume remains consistent. This study aims to investigate the feasibility of using optical tracking for real-time quality control of active breathing coordinator (ABC)-assisted deep inspiration BH (DIBH).
  
  
  METHODS
  An in-house optical tracking system (OTS) was used to monitor ABC-assisted DIBH. The stability and localization accuracy of the OTS were assessed with a ball-bearing phantom. Seven patients with left-sided breast cancer were included. A free-breathing (FB) computed tomography (CT) scan and an ABC-assisted BH CT scan were acquired for each patient. The OTS tracked an infrared (IR) marker affixed over the patient's xiphoid process to measure the positional variation of each individual BH. Using the BH within which the CT scan was performed as the reference, the authors quantified intra- and interfraction BH variations for each patient. To estimate the dosimetric impact of BH variations, the authors studied the positional correlation between the marker and the left breast using the FB CT and BH CT scans. The positional variations of 860 BHs as measured by the OTS were retrospectively incorporated into the original treatment plans to evaluate their dosimetric impact on breast and cardiac organs [heart and left anterior descending (LAD) artery].
  
  
  RESULTS
  The stability and localization accuracy of the OTS was within 0.2 mm along each direction. The mean intrafraction variation among treatment BHs was less than 2.8 mm in all directions. Up to 12.6 mm anteroposterior undershoot, where the patient's chest wall displacement of a BH is less than that of a reference BH, was observed with averages of 4.4, 3.6, and 0.1 mm in the anteroposterior, craniocaudal, and mediolateral directions, respectively. A high positional correlation between the marker and the breast was found in the anteroposterior and craniocaudal directions with respective Pearson correlation values of 0.95 and 0.93, but no mediolateral correlation was found. Dosimetric impact of BH variations on breast coverage was negligible. However, the mean heart dose, mean LAD dose, and max LAD dose were estimated to increase from 1.4/7.4/18.6 Gy (planned) to 2.1/15.7/31.0 Gy (delivered), respectively.
  
  
  CONCLUSIONS
  In ABC-assisted DIBH, large positional variation can occur in some patients, due to their different BH maneuvers. The authors' study has shown that OTS can be a valuable tool for real-time quality control of ABC-assisted DIBH.
authors.affiliation: Department of Radiation Oncology, College of Medicine, University of Florida, Gainesville, Florida 32610 and J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, Florida 32610.
authors.forename: Kathryn E
authors.initials: KE
authors.lastname: Mittauer
authors.affiliation: Department of Radiation Oncology, College of Medicine, University of Florida, Gainesville, Florida 32610.
authors.forename: Rohan
authors.initials: R
authors.lastname: Deraniyagala
authors.affiliation: Department of Radiation Oncology, College of Medicine, University of Florida, Gainesville, Florida 32610.
authors.forename: Jonathan G
authors.initials: JG
authors.lastname: Li
authors.affiliation: Department of Radiation Oncology, College of Medicine, University of Florida, Gainesville, Florida 32610.
authors.forename: Bo
authors.initials: B
authors.lastname: Lu
authors.affiliation: Department of Radiation Oncology, College of Medicine, University of Florida, Gainesville, Florida 32610.
authors.forename: Chihray
authors.initials: C
authors.lastname: Liu
authors.affiliation: Department of Radiation Oncology, College of Medicine, University of Florida, Gainesville, Florida 32610.
authors.forename: Sanjiv S
authors.initials: SS
authors.lastname: Samant
authors.affiliation: Department of Radiation Oncology, College of Medicine, University of Florida, Gainesville, Florida 32610.
authors.forename: Judith L
authors.initials: JL
authors.lastname: Lightsey
authors.affiliation: Department of Radiation Oncology, College of Medicine, University of Florida, Gainesville, Florida 32610.
authors.forename: Guanghua
authors.initials: G
authors.lastname: Yan
mesh_terms: D000368:Aged; D001940:Breast / Q000528:radiation effects*; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D062485:Breath Holding; D019583:Dose Fractionation, Radiation; D005240:Feasibility Studies; D057918:Fiducial Markers; D006801:Humans; D007259:Infrared Rays; D008875:Middle Aged; D058958:Organs at Risk / Q000528:radiation effects; D019047:Phantoms, Imaging; D011874:Radiometry; D011880:Radiotherapy Planning, Computer-Assisted; D011881:Radiotherapy, Computer-Assisted / Q000009:adverse effects / Q000592:standards*; D014057:Tomography, X-Ray Computed