title: Deep inspiration breath-hold radiotherapy for lung cancer: impact on image quality and registration uncertainty in cone beam CT image guidance.
abstract: OBJECTIVE
  We investigated the impact of deep inspiration breath-hold (DIBH) and tumour baseline shifts on image quality and registration uncertainty in image-guided DIBH radiotherapy (RT) for locally advanced lung cancer.
  
  
  METHODS
  Patients treated with daily cone beam CT (CBCT)-guided free-breathing (FB) RT had an additional CBCT in DIBH at three fractions. These CBCT scans were offline rigidly registered (on tumour) to FB and DIBH CT scans acquired at planning. All registrations were repeated to evaluate the intraobserver uncertainty. CBCT scans were scored on degree of streak artefacts and visualization of tumour and anatomical structures. We examined the impact of tumour baseline shift between consecutive DIBHs on CBCT image quality.
  
  
  RESULTS
  CBCT scans from 15 patients were analysed. Intraobserver image registration uncertainty was approximately 2 mm in both FB and DIBH, except for the craniocaudal direction in FB, where it was >3 mm. On the 31st fraction, the intraobserver uncertainty increased compared with the second fraction. This increase was more pronounced in FB. Image quality scores improved in DIBH compared with FB for all parameters in all patients. Simulated tumour baseline shifts ≤2 mm did not affect the CBCT image quality considerably.
  
  
  CONCLUSIONS
  DIBH CBCT improved image quality and reduced registration uncertainty in the craniocaudal direction in image-guided RT of locally advanced lung cancer. Baseline shifts ≤2 mm in DIBH during CBCT acquisition did not affect image quality. Advances in knowledge: DIBH RT has dosimetric advantages over FB; this work demonstrates an additional benefit of DIBH in terms of registration accuracy because of improved image quality.
authors.affiliation: 1 Section of Radiotherapy, Department of Oncology, Rigshospitalet, Copenhagen, Denmark.|2 Niels Bohr Institute, Faculty of Science, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Mirjana
authors.identifier: http://orcid.org/0000-0001-8288-162X
authors.initials: M
authors.lastname: Josipovic
authors.affiliation: 1 Section of Radiotherapy, Department of Oncology, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Gitte F
authors.initials: GF
authors.lastname: Persson
authors.affiliation: 1 Section of Radiotherapy, Department of Oncology, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Jens P
authors.initials: JP
authors.lastname: Bangsgaard
authors.affiliation: 1 Section of Radiotherapy, Department of Oncology, Rigshospitalet, Copenhagen, Denmark.|3 Faculty of Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Lena
authors.initials: L
authors.lastname: Specht
authors.affiliation: 1 Section of Radiotherapy, Department of Oncology, Rigshospitalet, Copenhagen, Denmark.|2 Niels Bohr Institute, Faculty of Science, University of Copenhagen, Copenhagen, Denmark.|3 Faculty of Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Marianne C
authors.initials: MC
authors.lastname: Aznar
mesh_terms: D062485:Breath Holding; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D019047:Phantoms, Imaging; D011880:Radiotherapy Planning, Computer-Assisted; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D035501:Uncertainty